In Chiang Mai tried to do my 90 day checkin online, because the online was down for so long, I had to do the last one at imm airport, the thing is because I did that, it won't allow me to do it on line got the "rejected" I have been doing it online for 18 months.
TLDR : Answer Summary
The poster is experiencing issues with their online 90-day check-in application in Chiang Mai, having received a rejection despite successfully using the online system for 18 months. They had to complete their last check-in at the immigration airport due to online downtime. Other users shared similar experiences, suggesting that the best option is to file in person again, with recommendations for locations and tips for a quicker process.