Unable to update email address of managed account

Hello @suthawan jirandorn 

That error usually means the new email is already in use by another Atlassian account, even if you cannot currently find it in your Managed accounts list. Atlassian only allows one Atlassian account per email address.

This behavior is specifically described in official KB Article for this:

https://support.atlassian.com/atlassian-cloud/kb/how-to-overcome-email-is-already-taken-error-when-trying-to-change-email-address-of-an-atlassian-access-managed-account/ 

Note that Apply when Account are managed. By Basic only 1 E-Mail Adress can be tied to Account. That's what generating this problem.