Error 500 on api request

Hello all, yesterday i took forge and linode and started my laravel 5 app. I am going to make an api something like payment handlers (that update inventory when user pay successfully) . When I visit the url by myself (for testing) it is working but when payment processor api trigger that url it getting error 500 .

While i know payment api is correct because when i use share hosting for testing purpose the payment api trigger by payment processor successfully.

So please help

Regards