That is what the officer told me. Most likely to prove that I am not married just to get a visa and not involved in human trafficking and not related to detainees

It takes many steps and different requirements depends on the state. I needed bank statement that shows I have at least 400,000 Baht in a bank that is Thai for more than 2 months, single status proof from before marriage, marriage proof from my country, marriage certificate from the embassy in thailand that is translated to Thai and confirmed at the foreign affairs office, photo of me with her in her house and and with her parents from outside her house and in the house that includes living room, bed room and others. Copy of her father and her ID, registered address, their document to prove their job status, my job status, interview with police at her house with her and her father that proves that I live there (living in an apartment with her is not acceptable). I had to go to the immigration with her and her father 4 times and it took 3 month and costed 4000 baht