GST Invoicing for freelancer

Hi,

I am working as a software freelancer for an Indian company, 'A'. The exports the services that I provide to a foreign entity. Our work contract is done in US dollars. As per the contract, I am supposed to get $20 per hour for the services that I provide.

So, my question is

a. Can I raise an invoice or a bill to this Indian company 'A' in USD and get paid in INR at applicable conversion rates?

b. What precautions do I need to take while filing GST returns ?