Do I need to show proof of a return flight when entering Thailand on a 45-day tourist visa, and what are the current visa rules?

asked and answered a thousand times…

The answers are yes and yes.

Because if you can’t show to the person when you check in that you either have a return or any booking out of Thailand, then you might be denied boarding.

Immigration usually won't ask to see it, but the problem usually comes from your airline. They may not let you board your flight unless you can show proof of travel outside of Thailand within the 45 days you'll be stamped in, regardless of your intentions to extend.

You can try purchasing a cheap bus or train ticket out of Thailand within the 45 days, or Google "onward travel ticket" for other options