If a foreigner staying in the kingdom over 90 days without notifying residence to immigration officer or notifying later than the set period, must notify in person and a fine of 2,000.- THB will be collected. If a foreigner who did not make the notification of staying over 90 days is arrested, he/her will be fined 5,000.- THB with an additional fine not exceeding 200.- THB for each day which passes until the law is complied with.
https://bangkok.immigration.go.th/en/90days-report/