ArcGIS Field Maps: Unable to Open. Invalid argument

Error Message

Attempts to open a web map in the ArcGIS Field Maps mobile app fail and return the following error message:

Error:   
Unable to Open
Invalid argument.

Cause

The web map contains a route layer that has no origin or stop specified.

Solution or Workaround

Remove the route layer from the web map in ArcGIS Online

1. Log in to ArcGIS Online.
2. On the Content page, click the web map.
3. On the Overview tab of the item details page, click the Open in Map Viewer option.
4. Delete the route layer in the web map. Refer to ArcGIS Online: Manage and organize layers for instructions.

Set an origin and stop for the route layer

1. Log in to ArcGIS Online.
2. On the Content page, click the web map.
3. On the Overview tab of the item details page, click the Open in Map Viewer option.
4. On the Contents (dark) toolbar, click Layers and select the existing route layer.
5. On the Settings (light) toolbar, click Map tools and select Directions.
6. In the Directions pane, enter the route origin and a stop. Refer to ArcGIS Online: Create a route layer for further instructions.