When making a claim, the taxpayer should include the letter that closed the enquiry, settled the appeal by agreement, or sets out the decision of the Tax Tribunal.
Wrth wneud hawliad, dylai'r trethdalwr gynnwys y llythyr oedd wedi terfynu'r ymholiad, setlo'r apêl drwy gytundeb, neu sy'n nodi penderfyniad y Tribiwnlys Trethi.