Services to sez - gst rebate procedures

Hi All,

We are doing services to clients are in SEZ of various state and district. In this case how we have to pay GST and in which part we have to pay IGST or CGST & SGST. 

Also, like to know the rebate procedure to get the claim of the GST since it was paid for the services rendered to SEZ companies.

Looking forward the correct procedures to follow.