The form for adding an account manager, found under Account Management > Account Managers > Add Account Managers, incorrectly hides the Email Address field when the "No Line Assigned" option is selected from the Mobile Number drop down. Once the Email Address field is hidden, the form will not submit as it still requires the field to be verified and does not display an error message because that field is hidden. This issue can be worked around by selecting any other option from the Mobile Number drop down, entering the email address, then re-selecting "No Line Assigned" before submitting the form.
Browser: Firefox 84.0.1 on Windows 10
Furthermore, a string of "Same Origin Policy" errors can be seen in the console on this page.