Hi. Some MT(which stands for message type) are just the format of the transfer including all the data, like the MT202, which refers to a cover payment and you can only see numbers, codes, and information regarding the banks. A Mt199 Swift message is what I call a "chat" message. Basically you use this format when a transfer order has been sent and you want to "talk" to the beneficiary bank in order to sort out something, or to find out if funds have been applied, or whatever. But it can be used for any other purpose. For instance, a Mt199 could go;
We refer to our Mtxxx, date xxxxxx,
(input information regarding the orderer and beneficiary. amount, dates, blah, blah, blah)
and then, straight to the point, you just simply type the text of your question, or demand, or whatever, like, "Our customer reports funds have not been applied yet, please confirm transfer status"
Kind regards, (whoever)
The other bank will reply to you using the same format (most likely), so sooner or later, you will have an incoming Mt199 from them, like;
We refer to your mt199 date xxxxx and our Mtxxx date xxxx
information, codes, etc...
"We are holding funds, request (whatever additional information) in order to apply funds to beneficiary minus our charges. Please confirm IBAN number (for example)."
Best Regards, (whoever)
So basically, a mt199 is one person "talking" to another.