A Letter of Authorization for GST is an important document to share power. What's the Right Way to Structure a GST Authority Letter?The form can be filled offline but it must be uploaded online. All requirements and form-filling instructions are available in the utility. A comprehensive guide on drafting a Letter of Authorization for GST, its compliance needs, and the roles of an Authorized Signatory. A Consent Letter for GST is a formal document that indicates the property owner's approval for a business to operate from their premises. Information about Form 8821, Tax Information Authorization, including recent updates, related forms, and instructions on how to file. Step 1: Visit the GST portal and go to 'Services' > 'Registration' > 'New Registration'. Once you are authorised for GST Filing, use your SingPass to log in to myTax Portal under "Business Tax Matters" to file your organisation's GST return. To. The Authorised Officer.