Googling the term wiil show that it is in common use

Example:

MCHI Financial Billing and Collection Policy - Memorial Community ...
https://www.memorialcommunityhealth.org/.../MCHI Financial B...
Definition: Plain Language Summary means a written statement that notifies a Responsible Individual(s) that MCHI offers financial assistance under the FAP for .

hope it helps!

My take on this is that you don't need the "financial" part, that's implicit in either of the English terms. In Spanish, however, the word "factura" on it's own can mean "hechura," and since the term "factura financiera" is mentioned subsequently in your paragraph, I assume they've simply used "financiera" to be specific, and then logically "facturación financiera" also.

Of course, it could mean the "financial aspect of billing", but I don't see that as consistent with the term "factura financiera" used here.

One other thing, as far as I could tell with a brief Google search of "financial billing" [or "financial invoicing"], instances of the two words used together seem to exist largely as "financial/billing" or "financial [&] billing," or simply using "financial" in other non-modifying ways. I didn't find any authentic (i.e., not translated) English use of either invoicing or billing with the modifier "financial," and I don't really see what it would add.