Got mine yesterday. In my Amphur the requirement was to be married (Amphur Si Bun Rueang, Province Nong Bua Lamphu). Married a month ago requirements were to provide my marriage certificate, passport, translations from the British Embassy of my passport and a copy of the affidavit to say I could legally marry ( why as I am already married?).
Amphur then gave me a form which I had to take to my local Immigration office. On this form were various questions which Immigration needed to answer and then send back to my Amphur. No idea what was being asked. Took Immigration about 2 weeks to do this documentation and get it to my Amphur (no monetary charge for this).
Amphur then contacted me and all was completed yesterday. As others have said in some Amphurs there is no requirement to even be married. I would also add that it is likely some Amphurs would require a lot more documentation while others less after all this is Thailand.