Attachments added to a feature layer brought to ArcGIS Pro version 3.1.0 or later through a portal connection are inaccessible, and the "MacBinary archive" error is returned in the ArcGIS Field Maps mobile app on iOS devices.

Workaround

• Use an Android device to access the attachments in ArcGIS Field Maps.
• Add attachments in ArcGIS Online.
• Open the web map or feature layer in the ArcGIS Pro project and not from the portal connection. Add attachments in ArcGIS Pro and overwrite the feature layer.
• Use a version of ArcGIS Pro before version 3.1.

Steps to Reproduce