Richard, I've looked into this and I'm not sure why you can't store more than one person as a default in the people picker. I'm doing some more research.

When you say dynamic approver field, what do you mean by that - 'dynamic'.

Eric,

In one of my past projects on-prem with InfoPath I just passed the account names separated by semicolons and that worked ok. Since this is O365 I tried email addresses separated by semicolons but no dice. It works fine with one email address as the default however. Looking at the javascript values they just seem to be in an array. Maybe I just need to try other separators (like a comma since it is an array) or wrap them in quotes or something. I just figured a bunch of people on here had already dealt with it so I didn't spend a ton of time investigating.

Dynamic meaning the users can change who the workflow approvers are before they submit the form (they aren't static in the workflow or separate list).

Richard.... I'm looking into that. I agree it should accept those values separated by some separator. I've tested a bunch with no success, but will keep digging.

Bump, I still have a need for this if anyone knows how.