What additional documentation do I need to provide to verify my status as a freelancer for remote work in Thailand?

Anonymous participant Your responses are contradictory. If you submitted a letter from your boss, you attempted to tell the embassy that you work for him or the company he works for. However, it sounds like you do not plan to continue to work for him, but used a letter from him to get the visa. These are red flags to the embassy. Since it sounds like you told the embassy you are continuing to work for him, you need a letter from them, signed, stating you have permission to work remotely.

Anonym deltagare you are contradicting yourself in your post and by this comment...

"...my boss didn't wanna sign the statement as I'm not going to be an employee when I'm a freelancer."

and

"I sent my current employment contract and I will be working remotely for my company."

Either you will work remotely as an employee of a company outside Thailand... Then a work contract is valid information to send and the work contract needs to mention that you are allowed to work remotely (this is what the embassy is asking for).

OR

You you apply as a freelancer with clients outside Thailand. I guess this is what you are going to do and that your current employer is going to be your future client.

If that is the case you need to write an explanation about this to the embassy. If you are ending the work contract you sent, then it is not really a "base for your application". For that you need to show client contracts (one or more if you have).

So you need to make a client contract with the company where you have worked up until now. (It could mention that you've previously been employed and that they will pay for your services as a freelancer going forward. It should include what type of work you will do for them etc.)