I'm on a 30 day visa exemption + 30 day extension (Not Tourist Visa). I just renewed my USA passport and got it in the mail today.
I think I'm supposed to go to immigration to have my stamp transferred to the new passport now - but what happens if I don't and I just showup at the airport with both passports?
Is there a fine or anything?
Would like to save myself the extra trip to immigration if it can be avoided.
TLDR : Answer Summary
If you are leaving Thailand by air, there is no need to transfer your visa extension stamp to your new passport. However, if you were to apply for an extension or leave through a land border checkpoint, you would need to transfer the stamp. In this case, the individual can present both their old and new passports at the airport without facing a fine.