edit: NVM. The problem resolved itself. I tried again several hours later.
I thought I’d ask a related question here.
How long before my device EUI drops out of the system and is “allowed” to be added to a new account?
I deleted the device, then deleted my account (I observed the email address I used to signup was typed incorrectly.) I get the “conflict” error when I try to add the device EUI to my new account.