Bulk send: Adobe is not accepting the Recipient Type

Hello. 

I am testing the bulk send function but coming into errors that prevent me progressing.

- Once I upload a CSV for the bulk send I get an error stating that the Recipient_2:Role names are incorrent in my CSV. However, they are correct per the Adobe online guidance. The Recipient_2:Role Types in my file are ACCEPTOR and CERTIFIED_RECIPIENT.
- I also have a Recipient_1:Role as an APPROVER - there seems to be no issue with this. 
- It worked previously, when I had the Recipient_2:Role as SIGNER, but I do not want anyone to actually sign this document, only to receive it (following approval from the APPROVER).

Any suggestions? Could it be linked to how I have set up my template i.e. it is not possible to send my template without a signer? I haven't added a signature field into the template. 

Thanks in advance!