An error message, “There was an error” is returned when updating the list of values for a domain field in Portal for ArcGIS if the domain name already exists in the relational data store.

Workaround

1. Use ArcMap or ArcGIS Pro to rename the domain from the geodatabase properties.
2. Re-upload the zipped file, and publish a hosted feature layer.

Alternative workaround:

1. In ArcGIS Online, navigate to the item details page of the hosted feature layer, and click Data > Fields.
2. Select the desired field, and edit the description by filling it with a simple text.
3. Click Save and create the list of values.

Steps to Reproduce