Hello,
To enable this feature, you need to enable the options for it from the Admin CP, General Settings page.

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Then enable the following options according to your needs:

- Automatically Register Member as Vendor (Payplan Settings page): If you want to enable registered members as vendors (this will only apply to the new registered members after this feature is enabled).
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- Registered as Vendor (update member page): If you want to select specific members as the vendor.
Best Regards,