Sync via sFTP to standalone server - cant sync DB - permissions issue

[The G]

OK maybe an odd issue:
Using Business edition.
one domain server with a folder full of data
one sFTP standalone server with a twin folder full of data.
objection is to keep the two folders replicated.
Configured an sFTP user account on the sFTP server, to allow freefilesync to connect from the domain server to the standalone server to compare the two folders.
set up for a scheduled task to replicate between the two servers on a cycle
all works except that the scheduled task running from the domain controller, generates error messages that it cant access the sync.ffs_db file that it tries to create on the standalone, when syncing.
Pretty sure its because the task runs from the domain server, connecting to the standalone server, and the domain server doesnt have permissions on the standalone.
How can I get it to run, connecting via sFTP, but with credentials from the standalone, to be able to modify the sync db files on the standalone when it syncs
Image attached of the error messages.

Answers on a postcard, or here :)