Permissions on variable values

I am using Metabase v1.50.8
I want to have permissions to the filter values (multiselect variable values) of a dashboard, but can't seem to find a way.
I have different permission groups set up, and I have one dashboard with a multiselect variable called Partner that loads its values from a table.
Each group has to have access to only one partner. My current solution is having duplicates for the same dashboard and "hardcoding" the partner id in the sql queries. If I set up variable-level permissions so that each group is able to select the values on which they have permission, my problem will be solved, and I'll have only one dashboard.
Do you know a way to do this? Maybe we can have row-level permissions in the tables for groups?

Hi, you need sandboxing: Data sandboxes have you seen that feature already?

Yes, I tried the feature, but it doesn't seem to work on filters (multiselect variables). I have a variable that's linked to the table that I want to have row-level permissions to, but it seems like even after applying the sandbox rules, people are able to select any value from the variable and see the dashboard.
Am I doing something wrong? Does sandboxing also work on variable values?