upsertCustomerCustomAttribute only working after manually setting a value in Square web UI

I created the custom attribute manually via the square webpage. Then I got the custom attribute ID from getCustomerCustomAttributesApi so I can upsert the attributes value.

So, since the attribute is already created through the website, I assume I don’t need to run CreateCustomerCustomAttributeDefinition? Or are you saying that I need to create a definition of each attribute for each customer record?

Does my question make sense?