And, though it should have worked, it went wrong at BKK on my way out as Chiang Mai immigration stamped the wrong frigging date. Always check your stamps right away.
I know people are renewing. And if they can do it once then they should be able to do it twice. That will give you 90 days. I did that once and then applied for a 7 day extension at the end of that period. It still cost 1900 baht though!
When you fly out, it's the destination's rules that obtain, ie. Thailand's. But you will also need a negative PCR or antigen test result before you return to the UK - a 48 hour one as opposed to the 72 hour one required by Thailand. Message KLM here. They will respond:
I had everything done too! No rejections nor resubmissions required in the application process. I had everything printed. Twice. That wasn't my problem. I'm just telling you what happened despite my excellent preparation and planning. Even Emirates didn't know in retrospect that I'd flown on three, as opposed to the two flights I actually booked. It's a shit-show.