Add field to Feature Layer with Relationship

[kapalczynski]

I have taken ownership of some hosted data that has a relationship class to a table.  

1. When I am in ArcGIS Online to go to the feature layer and click it
2. I go to Data Tab and select the Layer in the layer box
3. I then hit the three bars (Options) but the "Add Fields" button is not there

I assume this is because of the Relationship?  I go to another Hosted Feature Layer that does not have a relationship and I can see the Add Fields button.  

If that is the case how to I add a field to a Hosted Feature Layer that has a relationship?

[kapalczynski]

[RyanUthoff]

I just tried this and the Add Fields button is visible for me for a hosted feature service with a relationship class. By any chance is your hosted feature service restricted from being able to add fields?