[API] How to create an agreement and specify a workflow

Hello guys,

I'd like to create an agreement via Adobe Sign's API and force it to use a specific workflow (created in Adobe Sign's Workflow Design page). The workflow is fairly simple, 2 users must sign the document for the workflow to be completed.

I struggled a bit with Adobe Sign's API, but I eventually ended up making it work for non-workflow based agreements. I can create an agreement based on a PDF document that includes signature fields, I add a recipient's email address, and it works great. But as soon as I start adding a workflow id in my API call (POST to /agreements), I get this error :

Error calling POST /agreements: PARTICIPATIONSET_LABEL_MISSING Empty label value for a participation set

What does this "label value" mean ? I read in the docs that it corresponds to the unique label of a participant set. What is a participant set exactly ? Further in the doc, they say "For custom workflows, label specified in the participation set should map it to the participation step in the custom workflow." What is this participation step and where can I find it ? I only have the following pages on the left side panel : Workflow Info, Agreement Info, Recipients, Emails, Documents and Sender Input Fields...

Do you have any idea where the problem could come from ?

Thanks in advance for your help !

Jonah