The error message, "Error: [999999, Something unexpected caused the tool to fail. Failed to Execute (Update Schema)]" is returned when adding a new field to a related table from a hosted feature service in ArcGIS Pro.
Last Published: November 1, 2019ArcGIS Pro
Bug ID Number
July 29, 2019
October 14, 2020
Operating System Version
The bug has been fixed. See the Version Fixed and Additional Information, if applicable, for more information.
In ArcGIS Online, navigate to the item details page and the hosted feature service data.