getting error while calling to OCTA get services

I have tried to call get validate session (using an OCTA API client) and it does not seem to always work: Sometimes it returns an invalid session error like the following:

 

{

"errorCode": "E0000005",

"errorSummary": "Invalid session",

"errorLink": "E0000005",

"errorId": "oaeOWI_EsKqTBqSijMqNcF11g",

"errorCauses": []

}

 

I am trying to get data like paging .

 

in 1st call , it is working great . url like "https://" + orgName + "/api/" + apiVersion + "/users";

 

In 2nd call i am passing "https://" + orgName + "/api/" + apiVersion + "/users?after=" + LastId + "&limit=200";

 

I am getting error in 2nd call in else statement.