On my (SharePoint 2013) sub site I have a list (where users from a specific store can report errors). This list I want to share with another group of users, those who will do something about the errors (entrepreneurs). I want them to be able to Edit in this list: they don't need delete and create items, just being able to change an item is fine.
The problem is, I don't want them to have access to the sub site itself, because there is information on the sub site that they don't need to know about, they should only see this list. So they don't have any access at all to the sub site, but I'm giving them permission to the list.
However, it seems like since they can't access the sub site, no matter what permission I give them to the list (Edit, Contribute, Full Control), in the end they only have Reading-access to the list and can't even update an item.
This error message turns up whenever they try to edit something in the list:
The entrepreneur group is external users, but that shouldn't matter, should it? I've added them to SharePoint groups with the right permissions.
Is there any possible way to solve this problem?