WordPress Membership Plugin
I got this error on a fresh install of wordpress and plugin.
I got this error because I created a member before creating a subscription.
To solve it I restarted the installation and in the simplemembership menus I started by creating a membership level and then the member by giving him this membership level and I no longer have the error.
There’s a bug in the plugin though, because if you have a member without a subscription level, the member’s edit form isn’t displayed in full, so you can’t modify or delete the misconfigured member.
Translated with DeepL.com (free version)