Cannot save the selection (in a grid)

 Hi ..I have used a grid to display data from DB and i want to select a row from it .But I cannot save the selected ID in to my rule input. Could you please help me with the error in my code below:

load(
  ri!gridPagingInfo: a!gridSelection(
    pagingInfo: a!pagingInfo(
      startIndex: 1,
      batchSize: 5,
      sort: a!sortInfo(
        field: "meetingID",
        ascending: true
      )
    ),
    selected: {}
  ),
  {
    a!billboardLayout(
      backgroundMedia: a!documentImage(
        document: a!EXAMPLE_BILLBOARD_IMAGE()
      ),
      backgroundColor: "",
      overlayStyle: "DARK",
      overlayContents: {
        a!richTextDisplayField(
          labelPosition: "COLLAPSED",
          value: {
            a!richTextItem(
              text: {
                "Hello, " & user(
                  loggedinuser(),
                  "firstName"
                )
              },
              size: "LARGE"
            )
          },
          align: "LEFT"
        )
      },
      height: "SHORT",
      marginBelow: "STANDARD"
    ),
    a!columnsLayout(
      width: "MEDIUM",
      columns: {
        a!columnLayout(
          contents: a!cardLayout(
            contents: a!richTextDisplayField(
              value: {
                a!richTextIcon(
                  icon: "briefcase",
                  color: "ACCENT",
                  size: "LARGE"
                ),
                char(
                  10
                ),
                a!richTextItem(
                  text: "Created Meetings",
                  size: "LARGE"
                ),
                char(
                  10
                ),
                a!richTextItem(
                  text: "Meetings created by me",
                  style: "EMPHASIS"
                )
              },
              align: "CENTER"
            ),
            link: a!submitLink(
              saveInto: a!save(
                ri!getMeetingData,
                rule!MMS_732504_GetDetailsbyloggedInUser(
                  ri!gridPagingInfo.pagingInfo
                )
              )
            ),
            height: "AUTO",
            marginBelow: "STANDARD"
          )
        ),
        a!columnLayout(
          contents: a!cardLayout(
            contents: a!richTextDisplayField(
              value: {
                a!richTextIcon(
                  icon: "suitcase",
                  color: "ACCENT",
                  size: "LARGE"
                ),
                char(
                  10
                ),
                a!richTextItem(
                  text: {
                    "Invited Meetings"
                  },
                  size: "LARGE"
                ),
                char(
                  10
                ),
                a!richTextItem(
                  text: {
                    "Meetings I'm invited to"
                  },
                  style: "EMPHASIS"
                )
              },
              align: "CENTER"
            ),
            /* Setting this variable would be used to navigate to a category of answers */
            link: a!submitLink(
              saveInto: a!save()
            ),
            height: "AUTO",
            marginBelow: "STANDARD"
          )
        ),
        a!columnLayout(
          contents: a!cardLayout(
            contents: a!richTextDisplayField(
              value: {
                a!richTextIcon(
                  icon: "tasks",
                  color: "ACCENT",
                  size: "LARGE"
                ),
                char(
                  10
                ),
                a!richTextItem(
                  text: {
                    "My Tasks"
                  },
                  size: "LARGE"
                ),
                char(
                  10
                ),
                a!richTextItem(
                  text: {
                    "Tasks assigned to me"
                  },
                  style: "EMPHASIS"
                )
              },
              align: "CENTER"
            ),
            link: a!dynamicLink(
              saveInto: a!save()
            ),
            height: "AUTO",
            marginBelow: "STANDARD"
          )
        )
      }
    ),
    a!columnsLayout(
      columns: a!columnLayout(
        a!boxLayout(
          label: "Meetings created by me",
          showWhen: if(
            isnull(
              ri!getMeetingData.data
            ),
            "No Meetings created",
            true
          ),
          style: "ACCENT",
          contents: {
            a!gridField(
              totalCount: ri!getMeetingData.totalCount,
              selection: if(ri!getMeetingData.totalCount >0,true,false),
              identifiers: index(
                ri!getMeetingData,
                "identifiers",
                null
              ),
              validations: if(
                count(
                  ri!gridPagingInfo.selected
                ) > 1,
                "Please select 1 booking at a time",
                ""
              ),
              columns: {
                a!gridTextColumn(
                  label: "Meeting ID",
                  field: "meetingID",
                  data: index(
                    ri!getMeetingData.data,
                    "meetingID",
                    null
                  )
                ),
                a!gridTextColumn(
                  label: "Subject",
                  field: "subject",
                  data: index(
                    ri!getMeetingData.data,
                    "subject",
                    null
                  )
                ),
                a!gridTextColumn(
                  label: "Details",
                  field: "description",
                  data: index(
                    ri!getMeetingData.data,
                    "description",
                    null
                  )
                ),
                a!gridTextColumn(
                  label: "Conducted On",
                  field: "startDateTime",
                  data: index(
                    ri!getMeetingData.data,
                    "startDateTime",
                    null
                  )
                )
              },
              value:ri!gridPagingInfo,
              saveInto: {
                ri!gridPagingInfo,
                a!save(
                  ri!selectedMeeting,index(ri!gridPagingInfo,"selected",null)        
                )
              }
            ),
            a!buttonLayout(
              primaryButtons: {
                a!buttonWidgetSubmit(
                  label: "Update",
                  value: cons!MMS_BUTTON_ACTIONS[1],
                  saveInto: {
                    ri!meetingAction
                  },
                  style: "NORMAL"
                ),
                a!buttonWidgetSubmit(
                  label: "Cancel",
                  value: cons!MMS_BUTTON_ACTIONS[2],
                  saveInto: {
                    ri!meetingAction,
                    a!deleteFromDataStoreEntities(
                      dataToDelete: a!entityDataIdentifiers(
                        cons!MMS_CREATE_MEETING_ENTITY_732504,
                        ri!selectedMeeting
                      ),
                      deletionComment: "selected meeting canceled"
                    )
                  },
                  style: "DESTRUCTIVE"
                )
              }
            )
          }
        )
      )
    )
  }
)