My Mexican tax accountant figured this out. He spoke with both AirBnb support and SAT. He has other clients who show two documents in Facturify. One document under International, and the other document under the regular section which he likes to call Domestic, although there is no section labeled Domestic. For those clients who have the same withholding certificate under both sections, that data is automatically transmitted to SAT. This is what your Mexican accountants are used to.
However, my withholding certificate was only under the International section. Therefore, my withholding certificate is not automatically transmitted to SAT. I am guessing this happens because I have the money sent to a US bank in USD, which is totally legal. However, this means that my Mexican accountant needs to download the .pdf’s from the International section and manually enter it into my account with SAT to receive credit for the withholding.
If you don’t have a Mexican tax ID, I don’t think you will be able to log into Facturify.
Hope this helps at least some of you. The problem is the complexity involved here. It is huge.