Please quote the law article.
Don't bother, I'll reply.
https://www.thailandlawonline.com/civil-and-commercial-code/521-536-gift-is-a-contract
Section 521. A gift is a contract whereby a person, called the donor, transfers gratuitously a property of his own to another person, called the donee, and the donee accepts such property.
A gift is a contract by itself.
Section 525. The gift of a property the sale of which must be made in writing and registered by such competent official is valid only when so made and registered by the competent official. In such case it is valid without delivery.
Section 526. If a gift or a promise for a gift has been made in writing and registered by the competent official and the donor does not deliver to the donee the property given, the donee is entitled to claim the delivery of it or its value, but he is not entitled to any additional compensation.
Both sections 525 and 526 imply gift has not to be necessarily made in writing, granted that a bigger stack of papers could ease things if audited.