Hi, golf clapp I want to help you with this question.
If I understand your question correctly, you created and verified a custom domain in the Email communication resource and tried to use this domain in the communication service afterward, right?
Your screenshots don't show the selected data location of the email domain but I assume there is the problem right now.
You need to verify that the data location of the created and verified domain in the email communication service resource is in the same geo-location as the communication service you want to create. Otherwise, the domain will be not available to select, as shown in the screenshot two.
The other settings look fine.
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