Any tips for troubleshooting email delivery issues from HCM Communicate Campaign?

Summary:

In a DEV pod we have a test HCM Communicate campaign activated and scheduled (one-time and no schedule). We run the processes (Evaluate Eligibility/Prepare Campaign Email/Send Campaign Email/Track Campaign Email Delivery). The Campaign correctly shows in the overview Total = 7 and delivery date; Audience Breakdown also shows 7 Audience Members); but emails were not delivered to those employees. Other emails (e.g. journeys, transaction approvals) are being generated and successfully sent from the same dev pod. Are there any specific profile settings required for HCM Communicate? I did not see any required in the Oracle