PO Workflow Email Signature Links Not Working

SOLVED

We're having some issues with the emails in Sage X3 in that when the user clicks on the 'Accept' or 'Reject' links, the purchase orders are not being signed in Sage.

We have the APPPOH parameter set to Yes in parameter values...

... and the WRKRMTDIR parameter is set, so the links can create the files needed for approving/rejecting. However, when we click on the links, it doesn't seem to be creating a file in the directory? This has worked before, but for some reason has stopped working recently.

Is there anything we should check? The recurring task AWRKSIG is active so should be picking up the files from the folder, but no files look like they are getting created.