In the Exchange Online Properties section in the Active Roles Web Interface, the Delegation tab has an Add button which is greyed out and not functional for all users:
This is expected functionality in Active Roles 7.3.3 and below versions. The Add button is only functional when working with a Non-Federated Tenant type.
The ability to add new delegations when working with a Federated or Synchronized Tenant Type is a new feature which was introduced in Active Roles 7.4.1.
Upgrade to Active Roles 7.4.1.