Does anyone have recommendation for custom fields as primary keys?

[James Cope]

We have an external system with job numbers which we need to map to our Jira tickets. To do this, I am using a single-line text field since the number fields add commas (another debate for another day). The issue is that a typo when entering the job number in the custom field could result in duplicates. There is a free Unique Regex app solution for the server product, but that does not appear to be available for cloud.

Does anyone have a recommendation on how I can achieve the equivalent result of a primary key so that duplicates cannot be entered in a Jira custom field?

Thanks, in advance, for any advice you can provide.

Best regards,