Currently, to have a related tabled tied to a feature, you need to create the relationship in the geodatabase in ArcGIS Pro, then upload the features to ArcGIS online. Once it is in ArcGIS Online, you cannot add additional related tables, or remove a relationship without making the changes in the geodatabase offline, then completely overwriting the hosted feature service. For some of our feature services, this would be a massive undertaking and would break many of our maps and configurations in ArcGIS Online.
There should be a method in ArcGIS Online to create and edit the relationships right in ArcGIS Online. This way, if we have a hosted feature service, and later want to add a related table, we can do that right in ArcGIS Online without going back to the geodatabase to create the relationship.
