I noticed the error after few successful iterations. Maybe some throttling in play from the server?

➜  ~ java -jar ~/Desktop/CowinVaccineAvailabilitySpeaker-1.2.1.jar
   ______              _          _    __                _               ___              _ __      __    _ ___ __           _____                  __
  / ____/___ _      __(_)___     | |  / /___ ___________(_)___  ___     /   |_   ______ _(_) /___ _/ /_  (_) (_) /___  __   / ___/____  ___  ____ _/ /_____  _____
 / /   / __ \ | /| / / / __ \    | | / / __ `/ ___/ ___/ / __ \/ _ \   / /| | | / / __ `/ / / __ `/ __ \/ / / / __/ / / /   \__ \/ __ \/ _ \/ __ `/ //_/ _ \/ ___/
/ /___/ /_/ / |/ |/ / / / / /    | |/ / /_/ / /__/ /__/ / / / /  __/  / ___ | |/ / /_/ / / / /_/ / /_/ / / / / /_/ /_/ /   ___/ / /_/ /  __/ /_/ / ,< /  __/ /
\____/\____/|__/|__/_/_/ /_/     |___/\__,_/\___/\___/_/_/ /_/\___/  /_/  |_|___/\__,_/_/_/\__,_/_.___/_/_/_/\__/\__, /   /____/ .___/\___/\__,_/_/|_|\___/_/
                                                                                                                /____/        /_/
2021-06-08 08:31:42.660  INFO 92483 --- [           main] c.c.c.CowinVaccineAvailabilitySpeaker    : Starting CowinVaccineAvailabilitySpeaker on gaurangpate-ltm.internal.salesforce.com with PID 92483 (/Users/gaurang.patel/Desktop/CowinVaccineAvailabilitySpeaker-1.2.1.jar started by gaurang.patel in /Users/gaurang.patel)
2021-06-08 08:31:42.665  INFO 92483 --- [           main] c.c.c.CowinVaccineAvailabilitySpeaker    : No active profile set, falling back to default profiles: default
2021-06-08 08:31:43.580  INFO 92483 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.ws.config.annotation.DelegatingWsConfiguration' of type [org.springframework.ws.config.annotation.DelegatingWsConfiguration$$EnhancerBySpringCGLIB$$64ac5fc2] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2021-06-08 08:31:43.652  INFO 92483 --- [           main] .w.s.a.s.AnnotationActionEndpointMapping : Supporting [WS-Addressing August 2004, WS-Addressing 1.0]
2021-06-08 08:31:43.915  INFO 92483 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 7021 (http)
2021-06-08 08:31:43.926  INFO 92483 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-06-08 08:31:43.926  INFO 92483 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.31]
2021-06-08 08:31:43.988  INFO 92483 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-06-08 08:31:43.988  INFO 92483 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1257 ms
2021-06-08 08:31:44.751 ERROR 92483 --- [           main] c.c.c.Bootstrapper                       : Error registering district info, note: PinCode feature will still work
2021-06-08 08:31:45.033  INFO 92483 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2021-06-08 08:31:45.099  INFO 92483 --- [           main] o.s.b.a.w.s.WelcomePageHandlerMapping    : Adding welcome page template: index
2021-06-08 08:31:45.356  INFO 92483 --- [           main] o.s.s.c.ThreadPoolTaskScheduler          : Initializing ExecutorService 'taskScheduler'
2021-06-08 08:31:45.378  INFO 92483 --- [           main] o.s.b.a.e.web.EndpointLinksResolver      : Exposing 2 endpoint(s) beneath base path '/actuator'
2021-06-08 08:31:45.404  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:31:45.405  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:31:45.427  INFO 92483 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 7021 (http) with context path ''
2021-06-08 08:31:45.432  INFO 92483 --- [           main] c.c.c.CowinVaccineAvailabilitySpeaker    : Started CowinVaccineAvailabilitySpeaker in 3.257 seconds (JVM running for 3.804)

2021-06-08 08:31:55.405  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:31:55.406  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:31:58.150  INFO 92483 --- [nio-7021-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-06-08 08:31:58.150  INFO 92483 --- [nio-7021-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2021-06-08 08:31:58.156  INFO 92483 --- [nio-7021-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 6 ms
2021-06-08 08:32:05.409  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:32:05.409  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:32:13.621  INFO 92483 --- [nio-7021-exec-3] c.c.c.service.CoronaVaccinationService   : registered a new pin code = 390022, age = 45
2021-06-08 08:32:15.405  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:32:15.411  INFO 92483 --- [pool-1-thread-1] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:32:15.803  INFO 92483 --- [pool-1-thread-1] c.c.c.task.NotifyVaccinationDetails      : Found 2 vaccination centres at PinCode = 390022
2021-06-08 08:32:15.803  INFO 92483 --- [pool-1-thread-1] c.c.c.task.NotifyVaccinationDetails      : Sorry no vaccine available for  age 45
2021-06-08 08:32:15.803  INFO 92483 --- [pool-1-thread-1] c.c.c.task.NotifyVaccinationDetails      : Search complete for PinCode = 390022


2021-06-08 08:32:15.803  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:32:25.406  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:32:25.407  INFO 92483 --- [pool-1-thread-2] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:32:25.519  INFO 92483 --- [pool-1-thread-2] c.c.c.task.NotifyVaccinationDetails      : Found 2 vaccination centres at PinCode = 390022
2021-06-08 08:32:25.520  INFO 92483 --- [pool-1-thread-2] c.c.c.task.NotifyVaccinationDetails      : Sorry no vaccine available for  age 45
2021-06-08 08:32:25.520  INFO 92483 --- [pool-1-thread-2] c.c.c.task.NotifyVaccinationDetails      : Search complete for PinCode = 390022


2021-06-08 08:32:25.520  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:32:35.409  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:32:35.411  INFO 92483 --- [pool-1-thread-3] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:32:35.533  INFO 92483 --- [pool-1-thread-3] c.c.c.task.NotifyVaccinationDetails      : Found 2 vaccination centres at PinCode = 390022
2021-06-08 08:32:35.534  INFO 92483 --- [pool-1-thread-3] c.c.c.task.NotifyVaccinationDetails      : Sorry no vaccine available for  age 45
2021-06-08 08:32:35.534  INFO 92483 --- [pool-1-thread-3] c.c.c.task.NotifyVaccinationDetails      : Search complete for PinCode = 390022


2021-06-08 08:32:35.534  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:32:45.408  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:32:45.410  INFO 92483 --- [pool-1-thread-4] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:32:45.526  INFO 92483 --- [pool-1-thread-4] c.c.c.task.NotifyVaccinationDetails      : Found 2 vaccination centres at PinCode = 390022
2021-06-08 08:32:45.526  INFO 92483 --- [pool-1-thread-4] c.c.c.task.NotifyVaccinationDetails      : Sorry no vaccine available for  age 45
2021-06-08 08:32:45.526  INFO 92483 --- [pool-1-thread-4] c.c.c.task.NotifyVaccinationDetails      : Search complete for PinCode = 390022


2021-06-08 08:32:45.526  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:32:55.409  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:32:55.410  INFO 92483 --- [pool-1-thread-5] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:32:55.546  INFO 92483 --- [pool-1-thread-5] c.c.c.task.NotifyVaccinationDetails      : Found 2 vaccination centres at PinCode = 390022
2021-06-08 08:32:55.546  INFO 92483 --- [pool-1-thread-5] c.c.c.task.NotifyVaccinationDetails      : Sorry no vaccine available for  age 45
2021-06-08 08:32:55.546  INFO 92483 --- [pool-1-thread-5] c.c.c.task.NotifyVaccinationDetails      : Search complete for PinCode = 390022


2021-06-08 08:32:55.546  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:33:05.410  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:33:05.412  INFO 92483 --- [pool-1-thread-6] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:33:05.544  INFO 92483 --- [pool-1-thread-6] c.c.c.task.NotifyVaccinationDetails      : Found 2 vaccination centres at PinCode = 390022
2021-06-08 08:33:05.544  INFO 92483 --- [pool-1-thread-6] c.c.c.task.NotifyVaccinationDetails      : Sorry no vaccine available for  age 45
2021-06-08 08:33:05.544  INFO 92483 --- [pool-1-thread-6] c.c.c.task.NotifyVaccinationDetails      : Search complete for PinCode = 390022


2021-06-08 08:33:05.544  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:33:15.409  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:33:15.411  INFO 92483 --- [pool-1-thread-7] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:33:15.789 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:33:15.789  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:33:25.409  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:33:25.411  INFO 92483 --- [pool-1-thread-8] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:33:25.795 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:33:25.795  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:33:35.408  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:33:35.409  INFO 92483 --- [pool-1-thread-9] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:33:35.796 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:33:35.797  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:33:45.409  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:33:45.410  INFO 92483 --- [ool-1-thread-10] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:33:45.755 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:33:45.755  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:33:55.407  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:33:55.409  INFO 92483 --- [pool-1-thread-1] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:33:55.758 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:33:55.758  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:34:05.410  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:34:05.410  INFO 92483 --- [pool-1-thread-2] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:34:05.755 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:34:05.756  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:34:15.412  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:34:15.413  INFO 92483 --- [pool-1-thread-3] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:34:15.896 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:34:15.896  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:34:25.410  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:34:25.411  INFO 92483 --- [pool-1-thread-4] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:34:25.905 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:34:25.905  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:34:35.412  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:34:35.413  INFO 92483 --- [pool-1-thread-5] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:34:35.947 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:34:35.947  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:34:45.412  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:34:45.413  INFO 92483 --- [pool-1-thread-6] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:34:45.757 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:34:45.757  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
2021-06-08 08:34:55.410  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Checking vaccine availability for requested pin codes and districts
2021-06-08 08:34:55.411  INFO 92483 --- [pool-1-thread-7] c.c.c.task.NotifyVaccinationDetails      : Looking for eligible vaccination centres at PinCode = 390022
2021-06-08 08:34:55.805 ERROR 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Exception = org.springframework.web.client.HttpClientErrorException$Forbidden: 403 Forbidden: [{"message":"Forbidden"}]
2021-06-08 08:34:55.806  INFO 92483 --- [   scheduling-1] c.c.c.service.CoronaVaccinationService   : Successfully Checked vaccine available for pin codes and districts
^C2021-06-08 08:34:57.875  INFO 92483 --- [extShutdownHook] o.s.s.c.ThreadPoolTaskScheduler          : Shutting down ExecutorService 'taskScheduler'
2021-06-08 08:34:57.893  INFO 92483 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'