Troubleshooting Customer Attribute Relations Setup

My Customer Attribute relations don't work, how can I check if anything is not configured correctly?

We'd recommend you check which attribute is used as a parent attribute in the relation. Customer Attributes relations could be created only for parent attributes with the following types: 
  1. Multiple Select; 
  2. Dropdown; 
  3. Multiple Checkbox Select with Images; 
  4. Single Radio Select with Images.