What is the process for extending a tourist visa at Promenada, Chiang Mai?

An FYI in respect of extending a tourist visa at Promenada, Chiang Mai.

Arrived at 13:00 (Monday). Queue outside the immigration office (the actual outside between the two malls, not at the seats inside the mall, initially made that mistake). They check your paperwork, take your cash and give you a ticket.

One thing to note is that they won’t accept passport photo sized photos, you have to get the bigger ones (฿200 at the copy shop next door).

You then go inside and wait for your number to be called. It’s a lot slower than my experience at the Phuket office. Whole process took about 3.5hrs - I think there were about 60 numbers in front of me (30 mins in initial Q, 3hrs once I had a ticket).

They also don’t seem to be fussed about what you are wearing.