500-Internal server error when deploying RESTful API to IIS

Question

When using Postman with this GET

 localhost:28760/api/MotorCashiering

I was able to get the Status 200OK. But, after deploying to to my server (IIS) using this url: 

mysite/api/MotorCashiering

I get the 500 error. Can someone shed light to this error? Thanks a lot.