+1
OP was asking about Transmit, not Transmission
Transmit 5 is a complete rewrite of the original app and the old Transmit 4 workflows no longer work. Panic (the app author) has released a new service called Panic Sync. I believe a new workflow would need to interface with this service if an API is made available. I've reached out to their Team a few days ago but have not heard back. I'll post back if I hear anything.