The cross border flow implies the cross-border payments that are made between two countries.
The B2B (Business-to-Business) cross-border payments market is huge! No one has an exact estimate, but it is believed to be more than US$ 50 Trillion and probably closer to the US$ 100-125 Trillion mark per annum.
Suffice to say it is over the US$ 100 Trillion mark and that is what the report is referring to.
I did a video on the same subject a few months ago.