Maybe your marriage affirmation has the amount of your income in it. The current UK and Australian marriage affirmation does not state the monthly/annual income anymore. The embassy however provide you a letter explaining why.
It is basic requirement that a Male party needs to show proof of support for the female party. If the Male party is Thai, he also needs to show that proof.
You can show them the letter from the UK embassy explaining why your income was not stated in the affirmation and then show them your payslip or anything to support the OCCUPATION stated in your affirmation.
The check in counter will open 12:30am so I don’t think you will be able to pass immigration before midnight. Don’t worry, if you pass immigration around 1 or 2am you won’t be paying an overstay fine.
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.