Hi Devan, welcome to the Community. I am not sure what you mean by “...not the system”. You certainly can add custom fields of many types and associate them to projects and issuetypes. Regarding assigning issues to “customers” you can only assign issues to users that are licensed in Jira. So if you want to assign an issue to a customer you must first add them as a user. Now maybe you are wanting to add a custom field where you can place the customers name? If so you could use a text field for that.
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