a!dropdownField and Portals

I am trying to use a dropdownField in a portal interface.  The documentation says that it is compatible, yet I am getting an error message in the editor as well as the Portal configuration that the feature is not compatible.  Is there something special you have to do to get the dropdownField to work in a portal?

Here is the code for my DropdownField

 a!dropdownField(
        label: "I am applying for the following Event",
        labelPosition: "ABOVE",
        placeholder: "-- Please select the event you are applying for. --",
        required: true,
        choiceLabels: local!events['recordType!PMSO Event.fields.event'],
        choiceValues: local!events['recordType!PMSO Event.fields.eventId'],
        value: ri!volunteerRequest['recordType!PMSO Volunteer Request.fields.eventId'],
        saveInto: ri!volunteerRequest['recordType!PMSO Volunteer Request.fields.eventId'],
        requiredMessage: "Please select the event you are applying for!",
        searchDisplay: "AUTO"
      ),

The expression rule that loads the events into the local variable. According to the documentation, the a!queryRecordType is also compatible with a portal.

a!queryRecordType(
  recordType: 'recordType!PMSO Event',
  fields: {
    'recordType!PMSO Event.fields.eventId',
    'recordType!PMSO Event.fields.event'
  },
  
  pagingInfo: a!pagingInfo(
    startIndex: 1,
    batchSize: 100,
    sort: a!sortInfo(
      field: 'recordType!PMSO Event.fields.event',
      ascending: false
    )
  )
).data