API Request Time Out

I did project in Laravel then I register and verify user through API request from VB.Net Application, It works fine at first time. After some hours whenever I try it returns "request time out", if I made any change on controller in the server and tried again then it works perfectly. After some hours again it shows the same error. I tried lot of times the same problem was repeated again and again, after modification made on server it works fine. The modification I made in controller like returning echo message

eg:- "Status:Success" => "Status:Fine"

What is the problem I can't understand it