I am going to transfer money to buy a condo in Bangkok. Do I have to state specifically the unit number of the condo unit that I'm buying?

It depends only on developer. YOu'd better ask them. As I can understand you are going to remit from off-shore.. In my case I stated only Contract number and date, nothing more.

It depends on your bank.

I just stated that the funds transferred were "to purchase a condo" and the bank asked for a copy of the contract.

Be as vague as possible just in case there's a change in plan.

My unit was already designated and the developer told me to list the unit number as well as say it was for a purchase of a condo. I had to overpay due to exchange rates. Better to pay US Dollars (in my case) rather then send baht (the back would have screwed me on the exchange rate). They wouldn't let me wire the majority and pay the rest when I signed the papers. After all was said and done, they gave me a refund. BUT luckily my wife kept an account in Thailand so I was easy to deposit the refund.

My unit was already designated and the developer told me to list the unit number as well as say it was for a purchase of a condo. I had to overpay due to exchange rates. Better to pay US Dollars (in my case) rather then send baht (the back would have screwed me on the exchange rate). They wouldn't let me wire the majority and pay the rest when I signed the papers. After all was said and done, they gave me a refund. BUT luckily my wife kept an account in Thailand so I was easy to deposit the refund.

You must ONLY send foreign currency, not Baht.

But you were paying to the developer which is probably why he said to state the unit number, to make it easier for his records.