Civil and Commercial Code section 456 requires a completed immovable-property sale to be in writing and registered. Failure to meet that form makes that completed sale void.
A preliminary agreement to buy and sell is a different issue with its own evidential requirements. A payment receipt alone should not be treated as proof of registered ownership.
Practical checks: confirm signing authority, registered burdens, parcel details, payment arrangements and handover terms before completion.
Source: กรมที่ดิน — คู่มือการจดทะเบียนสิทธิและนิติกรรมเกี่ยวกับการโอน (ประเภทขาย) https://www.dol.go.th/media/813280771027636224/2026/01/JcYZ6ULfuAe5t2nXqoxMg8Dm.pdf
General information; sources checked on 5 November 2026. This is not case-specific legal advice. Confirm the applicable law and facts with the land office or a qualified professional.