Recipient Info is missing

We are using the Adobe Sign integration for MS Dynamics 365

We have followed the instructions in the "Adobe Sign for Microsoft Dynamics Online installation and configuration guide" for configuring a custom entity but when we Request Signatures the notification "Recipient Info is missing" appears and the Recipient details are not automatically populated as we would expect.

We suspect this is a configuration issue, but have run out of places to look. 

Has anyone experienced this issue and is able to offer advice please?