[Visa extension]
For your information I was able to extend (first extension) my visa for one month (until 26th of October) without having any letter from my embassy nor medical certificate. I went to the immigration service in Chiang Mai - Promenada, with the usual requested documents for extension plus the TM30 (notification form of residence) and paid the 1,900 THB. I am French nationality but I guess it doesn't matter.
Good luck everyone 🍀
TLDR : Answer Summary
This post discusses a successful one-month extension of a visa in Chiang Mai without requiring an embassy letter or a medical certificate. The user shared their experience, mentioning the standard documents needed for the extension, including the TM30 form and a fee of 1,900 THB. The comments provide clarification on different types of extensions, the necessity of paperwork, and variations in immigration requirements across offices, highlighting that experiences can differ depending on the type of visa and the specific immigration office visited.