Hi,

The developer wants to charge me extra for "late payment" for the contract I paid and complete 2 years ago.

Is this % amount regulated in Thailand or defined solely by contract ?

Answer to my own question:

Up to 15% or 7.5% by default: http://www.eulerhermes.com/products-solutions/debt-collection/Land-of-payment/Pages/thailand-collection-profile.aspx

How can you incur a late charge on a contract

Paid two years ago??