Postbox 5 integration vanished

Since I upgraded to OmniFocus 3, the OmniFocus contextual menu has disappeared from Postbox 5. I suspect that integration is alive and well in Postbox 6, but I can’t upgrade to v6 because they’ve dropped add-on support. Is there any way to get the contextual menu back? Thanks.

It doesn’t work with postbox 6 either. I emailed omnigroup about this on the 27th of October 2018, but haven’t received a reply yet.