Contingent workers can't have supplier portal user with same email ID/user

Summary:

Client uses contingent workers(CWK) functionality in expenses module who are setup as CWK in HR module.

In order to create suppliers for them, client would like to get them registered using supplier portal.

When tried to create supplier record from the supplier portal with the same user ID/email ID, it throws error as user name already exists which was created when CWK is created in HR module.

Can someone advise if it is possible for contingent workers to use supplier portal to create their supplier record so they can use expenses module.

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