even if I give him the jira service management access, I can't find him in the customer portal page (Neither active nor inactive)
If the user is a Jira user, it's not going to appear under the "Customers" menu voice.
You should go in the Project settings -> People in which there is the list of Jira users who have access to the project. From there, you can assign the role to the user (Admin, Service Desk Customer etc).
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