Gst registration

Hi All,

I need to get GST registration but i can't figure it out under which services it pertaining.

Business is Providing attestation of documents to public.

Accept the documents in Kerala and sent it to the main branch in Mumbai , all the payment is made through online by customers.

Since the service is provided from Mumbai inter state supply will attract so need to get the registration.

So which service should i categories it ,the rate of GST.

Please provide your valuable feedback.