What are the financial requirements for extending a Mon-O marriage visa in Thailand beyond the initial 90 days?

To extend a Mon-O marriage visa past the initial 90 days, you can refer to unofficial resources like the Phuket Immigration Volunteers site which states the financial requirements. You need to demonstrate either an income of 40,000 baht for 12 months prior to application or have 400,000 baht in a bank account in your name for 2 months prior to the application. Additionally, if you are employed, a letter from your employer may be necessary. For official guidelines, the Thai Immigration website provides relevant information that can be located under section 17.