Which certificate does the person asking actually want?
Ask them. A bank onboarding a corporate account, a client running supplier due diligence and a foreign tax authority applying a treaty all want different documents, and all three will say "your tax certificate".
Five minutes establishing which one is wanted saves a fortnight of sending the wrong document back and forth.
- Corporate tax certificate: proves registration
- VAT certificate: proves VAT registration and TRN
- Tax residency certificate: for treaty relief
- Ask the requester which they need