When should I extend my STV visa in Thailand and what documents are needed?

And the STV requirements from Division 1 immigration ("Bangkok immigration")

>When do I have to go to extend the visa?

At most immigration offices, when you have 30 days or less remaining on your entry stamp.

>Can I go to every immigration office or just selected once?

The immigration office where you live and have the TM 30 filed

>And the most important, what do I need to extend my visa?

You might not like this answer:

Here's a recent report I received from Nontaburi office:

I was in Nonthaburi to extend my STV visa. Here's what the officer asked...

1. Copy of passport

2. Copy of TM6

3. Copy of STV visa page on your passport

4. TM7, use the last updated one or get it from Immigration Office. With a photo affixed.

5. STM 2. Declaration that you're aware about overstay and the penalties.

6. ASQ certificate letter stating that you've completed 14 days quarantine.

7. Some kind of proof that you indeed stayed at the ASQ, i produced my ASQ hotel receipt ( room charges )

8. Health Insurance showing coverage amount, line by line items in details of IP, OP, Covid coverage amount.

9. Rental. To state clearly rental period when to when, at where, 4 signatures either passport or Thai ID at the end of agreement ( the usual standard contract ). If the rental's address is in Bangkok, you can only extend visa in Bangkok. Rental period should cover at least 3 months more.

And sign at every page."

They are also willing to accept a pre-booked, prepaid hotel with the property owner's Tax ID number, or your property certificate if you live in a condo.