GST applicability on payment

What type of services you have provided ?.

Clinical research services

Services provided out of India is treated as export of service and same is Zero rated under GST and two methods to export .

1) You can export with payment of IGST and later on claim refund .

2) You can export with LUT ( Latter of Under taking ) without payment of tax , subject to conditions.
also company in USA should not be sister concern of Your Indian company.

Ok, thank you very much for your time and assistance Mr. Prasad.
Have a nice day! :)

This is termed as export of service under GST. If you have LUT then you can provide this service without payment of GST (Do mention LUT number on the bill in this case). If you do not have LUT then you can sell by paying IGST and claim the IGST amount as refund