Troubleshooting

Problem	What to do
Vendor sees "No groups available"	Tick Allow vendors to manage this group on at least one customer group.
The vendor option isn't on the group page	The group must be a Customer group, the store a marketplace, and the module on.
Vendor can't add a customer	Known gap. Add them yourself in Customers → User Groups.
Customer lost group prices everywhere	A vendor removed them from the group; membership is store-wide. Add them back.