With me the Bangkok bank app. did not work. After I removed vpn and virusscan app (Avast) it worked. After re-installing the vpn and virusscan, it kept working. Maybe worth a check if relevant 🤷♂️
Y'r last name is Dutch/Fries. If you have a Dutch passport, you still can get an income statement (Visumondersteuningsbrief in Dutch) from the Dutch Embassy in BKK.
And I think you mean getting a year extension (instead of mentioning a non imm. O-A). With y'r imm non O, you should be able to open a bank account (if you not already have it) and indeed put the money ((800k฿) 2 months before applying for that year extension).
If you apply in y'r home country, you need the equivalent of 800,000฿ in y'r home bank account. The non imm. O-A visa, you ONLY can get in y'r home country.
Dit gaat puur over internet via de SIM. Het abonnement wat ik heb, is alleen 4G. Wat ik bedoelde met 'WiFi code' is dat ik op bijna alle plaatsen waar ik kom, daar de WiFi gebruik. Gebeurt trouwens automatisch als je al ooit een code hebt ingegeven.