FXP Server To Server Transfer Failing

Hi

I'm trying to use the server to server feature for the first time between 2 sites - no files are able to transfer, I wonder if there is a setting I am not using correctly or some other mistake I am making.

Error log:

[R] PASV
[R] 227 Entering Passive Mode (142,4,30,201,138,148)
[L] PORT 142,4,30,201,138,148
[L] 500 I won't open a connection to 142.4.30.201 (only to 188.29.19.183)
Site to Site Transfer Failed!
[R] Transfer Failed!

Any advice would be v helpful and appreciated!
Thanks