I am buying a new motorbike in Chiangmai with monthly paymentplan. Was told by shop have to get a document from Immigration. Immigration provides documents for this purpose. What kind of document do I ask for in immigration. Thank you. Johannes

You likely require a proof of address and if on an extension of stay from immigration they may provide. If not your Embassy may.

What you need is a Residence Certificate. Some Immigration Offices will not issue these any more. As said your Embassy probably will.

Here is the application form for Immigration.

res_cert.doc

As above form.

I just got this last week in Chiang Mai and purchased a bike for my gf but in my name, so no issue at all.

My girlfriend did fill out a form stating that I was staying with her though, so not sure if that made a difference. This was not done at the man immigration building but at the back behind the shop (where you get the photos taken).

Note I am not currently in CM and back in Aus. I was on a 30 day visa exempt at the time.

My name was added to my gf's lease though and we had a copy of that.

Chiang Mai Immigration issues these letters 500 baht, 2 passport photos and verification of your residency address.