The Smart Editor widget is an extension of the Edit widget in Web AppBuilder for ArcGIS, which provides the ability to edit a series of features and move or modify existing geometries. In some instances, when specifying an attribute value for a field using the Smart Editor widget, the field displays a drop-down list of selectable attributes, preventing users from inserting a custom attribute value. When attempting to edit the field with attributes other than the attributes listed in the drop-down list, the following message is returned:
Warning: The value entered is not valid.
This is by design. If a feature layer is assigned with symbology based on a field before publishing to ArcGIS Online, the attribute values that can be specified for the field in the Smart Editor widget are restricted to the associated attributes shown in the drop-down list.
To resolve this issue, symbolize the feature layer using the Single symbol symbology in ArcMap, and republish the hosted feature layer to be used in the Web AppBuilder for ArcGIS application.
The drop-down arrow is no longer visible for each editable field. The figure below shows the editable field in the Smart Editor widget with no drop-down values.