Flow Designer - "Internal Server Error"

[Gauri9]

Hello All,

I have a flow designer which triggers notification weekly on Friday. 
I have set following flow variables - 

* Offset -0 

* Limit - 400 

* hasMore - True

*Counter  - 0 

Next step gets the OAuth token from the endpoints provided and retrieves data from the API.

Next step creates staging records based on the data received from the above step.

Next step also creates alert records from the staging table.

Again setting the flow variables and the flow ends if the record count exceeds the limit of 500. 
OAuth set up is the newly created action which runs successfully when tested separately. 
But, when I am trying to run the whole flow it is giving the  "Internal Server Error". 
I have checked the logs and it says unable to set the flow variables. 
I am attaching few snapshots below for better understanding. 

Thank you.