What a lovely place - welcome from across the border in Brustol.
But oh dear - you really should have checked before launching your STR business @Kevin3074 😀
1. you need planning permission for commercial use for the cabin
2. you need to understand the new STR regulations and licensing for Wales to ensure you can comply https://www.gov.wales/licensing-scheme-visitor-accommodation-wales
3. you need to have a fire assessment under the new fire regulations and make necessary adaptations to comply ie fire doors, safety locks
4. you will be taxed on any income you earn from your STR business you can look on the HMRC site for allowable expenses. Probably worth having an accountant for your first year at least