What is your nationality and how many days do you plan on being in Thailand when you return from India ?

There is no such thing as far as I know. The RE refers to a re-entry permit obtained to keep a Non O permission to stay "alive" when you leave Thailand during that period you are stamped in for.

@Mark *********

, don't forget you now need insurance for an O-A visa.

On what basis are you currently in Thailand ? What will you be applying for in Cambodia ?

Since my first visit to Thailand in 1996, on Visa Exempt, Tourist Visas and lately Non O based on marriage, averaging 3 visits a year, I have NEVER been asked for an onward or return ticket by an Immigration Officer. It has been a different story at check-in at Glasgow, all visits over 30 days have been queried by the staff. KLM were once on the verge of refusing me on a Visa Exempt, saying you can't stay 31 days, until I pointed out that I didn't get there until tomorrow !

If it was an official marriage ceremony at the district office, you can get a Non Immigrant O Visa based on that marriage which gives you a 90 day permission to stay.

NO. As long as you are on the correct visa, but trying to live in Thailand on tourist visas and extensions is a bad idea.

Don't forget, you'll need to meet the new health insurance requirements on an O-A visa.

My advice, go early.

It says "IN UK" !