Our members do not login to the website. There is no member only content in it. But we want our members to be able to renew online. All members have a unique member number. We put their number on the label of the magazine we mail them, so they have it. It's stored in CiviCRM as Individual: External Identifier.
When we starter with CiviCRM we did not have email addressees for most members, so the email address in the CRM is often not real.
Is it possible to make a custom renewal form that accepts the member number and email address, and have a dedupe rule based on the member number? The email address should then be added (updated?) to the member record.
I tried making a copy of the New Member Form, and changed the profile to one that only asks for email and member number. But upon the form submit it returns this warning:
Please correct the following errors in the form fields below: External ID already exists in Database.
Any ideas what we should try next?
The environment is: Joomla: 3.9.14 CiViCRM: 5.21.1