No, you have to have the money in a Thai bank account for proof of funds for the extension in Thailand. The only time you use your home country bank account is for the initial visa you apply for online from the Thai Embassy in your country.
Yep, happened to me a couple days ago. I can’t increase more than 50,000. My Thai wife tried her app and was able to increase hers. She set it at 500,000 with no problem.
Some banks are very wary of international transfers. I have Navy Federal Credit Union and had no problem doing a wire transfer. I guess individual experiences will differ.
For small amounts I use the Wise or Remitly app. For amounts like 800,000 baht, I do a wire transfer from my home bank to my Thai bank using my Thai bank’s SWIFT code.