To file an application for claim of refund. 5. Step 1: Visit the GST portal and go to 'Services' > 'Registration' > 'New Registration'.A Consent Letter for GST is a formal document that indicates the property owner's approval for a business to operate from their premises. Of credit, such as a letter of credit. 21. Telephony Designator Assignment. 1-4-1. A letter of authorisation for GST is an essential document regarding taxation and business operations.