What documents are needed for extending a DTV in Thailand, and what should I wear for my appointment?

Just sharing my experience today at Bangkok Immigration in case it's useful to other DTV holders.

I went in to transfer my DTV stamp into a new passport and also had to pay a fine for a missed 90-day report. The whole process took quite a while, so be prepared for a long day if you're doing both.

What surprised me was when I asked about extending my DTV for another 6 months. As I'm on the business owner/workcation category, I was told I would need to provide quite a substantial portfolio of supporting documents, including:

Business documentation

Bank statements

Invoices

Evidence of ongoing business activity

Proof of 500,000 baht in my bank account for the previous 30 days

The officer then told me that an alternative would simply be to leave Thailand and re-enter, which would avoid the need for the extension application and supporting portfolio.

One other thing worth mentioning: I made the mistake of turning up in shorts. I've been coming to Thailand for 25 years and somehow forgot the importance of dressing smartly when dealing with government offices. The officer was not impressed and gave me a fairly stern lecture about it. Fair enough — lesson learned. Next time it'll be long trousers and a collared shirt.

Just posting this in case it helps anyone else planning a DTV extension in Bangkok. Has anyone else had a similar experience recently?

Just sharing my experience today at Bangkok Immigration in case it's useful to other DTV holders.