java.lang.NullPointerException after upgrading WSO2 API manager upgrade from 3.1.0 to 4.0.0 - wso2

Question

we have upgraded wso2 API manager from 3.1.0 to 4.0.0 using below link. During upgrade we did not see any error in logs.
https://apim.docs.wso2.com/en/4.0.0/install-and-setup/upgrading-wso2-api-manager/upgrading-from-310-to-400/
But we are getting error while access application end point after publishing to wso2 .
TID: [-1234] [] [2023-01-06 01:22:40,915] ERROR {org.apache.synapse.transport.passthru.ServerWorker} - Error processing GET request for : /pizzashack/2.0/menu. java.lang.NullPointerException
at org.wso2.carbon.apimgt.gateway.handlers.security.jwt.JWTValidator.<init>(JWTValidator.java:108)
at org.wso2.carbon.apimgt.gateway.handlers.security.oauth.OAuthAuthenticator.authenticate_aroundBody4(OAuthAuthenticator.java:130)
at org.wso2.carbon.apimgt.gateway.handlers.security.oauth.OAuthAuthenticator.authenticate(OAuthAuthenticator.java:115)
at org.wso2.carbon.apimgt.gateway.handlers.security.APIAuthenticationHandler.isAuthenticate_aroundBody42(APIAuthenticationHandler.java:428)
at org.wso2.carbon.apimgt.gateway.handlers.security.APIAuthenticationHandler.isAuthenticate(APIAuthenticationHandler.java:422)
at org.wso2.carbon.apimgt.gateway.handlers.security.APIAuthenticationHandler.handleRequest_aroundBody36(APIAuthenticationHandler.java:353)
at org.wso2.carbon.apimgt.gateway.handlers.security.APIAuthenticationHandler.handleRequest(APIAuthenticationHandler.java:317)
at org.apache.synapse.api.API.process(API.java:389)
at org.apache.synapse.api.AbstractApiHandler.apiProcessNonDefaultStrategy(AbstractApiHandler.java:107)
at org.apache.synapse.api.AbstractApiHandler.identifyAPI(AbstractApiHandler.java:127)
at org.apache.synapse.api.AbstractApiHandler.dispatchToAPI(AbstractApiHandler.java:59)
at org.apache.synapse.api.rest.RestRequestHandler.dispatchToAPI(RestRequestHandler.java:84)
at org.apache.synapse.api.rest.RestRequestHandler.process(RestRequestHandler.java:70)
at org.apache.synapse.rest.RESTRequestHandler.process(RESTRequestHandler.java:54)
at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.injectMessage(Axis2SynapseEnvironment.java:344)
at org.apache.synapse.core.axis2.SynapseMessageReceiver.receive(SynapseMessageReceiver.java:101)
at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
at org.apache.synapse.transport.passthru.ServerWorker.processNonEntityEnclosingRESTHandler(ServerWorker.java:375)
at org.apache.synapse.transport.passthru.ServerWorker.run(ServerWorker.java:189)
at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)