Selecting Hide My Email as my "from" address generates an error
I am trying to create a new Hide My Email address to send a message to a company. I've gone into the Mail section of iCloud.com and created a new message. I type the address I want to send to and then select the "from" field drop-down and choose "Hide My Email". At this point I get a dialogue overlay saying "{{Compose.Address.Fields.From.HideMyEmail.NeedToSetForwardingAddress.Title}}
":
When I click "OK" the "Hide My Email" text in the "from:" field has a ! before it, and I can't send the email:
How can I get Hide My Email to work?