ID Match integration from Enrollment Flows is currently designed for administrator driven flows. In order to support self signup flows, some additional changes are required:

1. Support for 202 Accepted responses (implying Match is configured for external rather than interactive match). This would require the flow to be handed off sort of like an approval step, but with the potential to hand back to the petitioner if later steps require it. This, in turn, might require Enrollment Flows Revision 3.
2. Verification of email addresses prior to match. Self service matching should not permit unverified email addresses. This implies duplicateCheck running after email confirmation, which is not compatible with administrator drive match, and might require running in multiple places (like T&C). This also might be better supported by Enrollment Flows Revision 3.