ArcGIS Enterprise: Execution error - Key not found. Verify test data

Error Message

When running an Arcade expression in a pop-up in Map Viewer, the following error is returned:

Error:
Test execution error: Execution error - Key not found - <fieldName>. Verify test data.

Cause

The display name or non-existing field name is used; for example, the field name is incorrectly spelled. The display name is only a label and cannot be referenced in expressions. Refer to Portal for ArcGIS: Set a display name or ArcGIS Online: Set a display name for more information.

Solution or Workaround

Verify that the field name is spelled correctly and matches the case in the attribute table. If the layer has no features, add at least one feature to ensure the field exists in the data. To create a new field, refer to Portal for ArcGIS: Add a field or ArcGIS Online: Add a field for instructions. The following image shows the display name and field name do not match.