Please can someone confirm that a re-entry permit can no longer be done at airport on the way out? Chaengwattana is the only place for Bangkok?

Is the visa you are on relevant to the reentry permit you apply for or how you go about it?

Many thanks in advance.

It should be obtained from the immigration office your extension of stay is from and costs 1k for single or 3.8k for multi re-entry. Most people now obtain at least a single when getting an extension of stay to be safe as airports do not issue except in extreme emergency situations. If you are here on a visa stay rather than and extension of stay you would normally use the office where located. Chiang Watanna Soi 7 would be the office in Bangkok. You fill out form/pay/provide photo and wait for it to be entered into your passport. On return you put that number in the visa field on arrival card and get the same permitted to stay date that you now have.

Thank you lopburi3!