The error message,  "Validation failed: Field does not contain unique values. Remove duplicates and try again" is returned while applying unique value constraints to a field in a hosted feature layer in ArcGIS Enterprise.

Workaround

When creating an index programmatically, make sure the name property is included in the addToDefinition payload. For example, {"indexes":[{"name":"test_index","fields":"state_name","isUnique":true,"description":"Field properties"}]}.

Steps to Reproduce