Required is not working in Grid

Required is not working for dropdown field in gridrow layout how can i resolve this ?

 a!gridLayout(
        label: "",
        labelPosition: "ABOVE",
        headerCells: {
          a!gridLayoutHeaderCell(label: ""),
          a!gridLayoutHeaderCell(label: "")
        },
        columnConfigs: {
          a!gridLayoutColumnConfig(weight: 3),
          a!gridLayoutColumnConfig(weight: 3)
        },
        rows: {
          a!gridRowLayout(
            contents: {
              a!textField(
                value: "Grantee Administrator (Primary Contact)",
                readOnly: true(),
                required: true()
              ),
              a!textField(
                showWhen: rule!SCO_isBoolNotEmptyAndTrue(ri!hasUserClickedGeneratePdf),
                readOnly: true,
                label: rule!GAI_utilFormatUserName(
                  ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{8852265a-0704-4a43-829a-c4828abf7234}usernameGranteeAdmin']
                )
              ),
              a!dropdownField(
                showWhen: rule!SCO_isBoolBlankOrEmptyOrFalse(ri!hasUserClickedGeneratePdf),
                placeholder: "---Select a value ---",
                choiceLabels: a!forEach(
                  items: local!granteeAdminUsers,
                  expression: rule!GAI_utilFormatUserName(usrName: fv!item)
                ),
                choiceValues: local!granteeAdminUsers,

                value: if(
                  or(
                    a!isNullOrEmpty(
                      ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{8852265a-0704-4a43-829a-c4828abf7234}usernameGranteeAdmin']
                    ),
                    a!isNullOrEmpty(local!granteeAdminUsers)
                  ),
                  null,
                  if(
                    contains(
                      local!granteeAdminUsers,
                      ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{8852265a-0704-4a43-829a-c4828abf7234}usernameGranteeAdmin']
                    ),
                    ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{8852265a-0704-4a43-829a-c4828abf7234}usernameGranteeAdmin'],
                    null
                  )
                ),
                saveInto: ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{8852265a-0704-4a43-829a-c4828abf7234}usernameGranteeAdmin'],
                required: true(),
                
              )
            }
          ),
          a!gridRowLayout(
            contents: {
              a!textField(
                value: "Grantee Financial Point of Contact",
                readOnly: true(),
                
              ),
              a!textField(
                showWhen: rule!SCO_isBoolNotEmptyAndTrue(ri!hasUserClickedGeneratePdf),
                readOnly: true,
                label: rule!GAI_utilFormatUserName(
                  ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{2409b484-c88f-406c-bacf-8094aabea5c7}usernameGranteeFiscalStaff']
                )
              ),
              a!dropdownField(
                showWhen: rule!SCO_isBoolBlankOrEmptyOrFalse(ri!hasUserClickedGeneratePdf),
                placeholder: "---Select a value ---",
                choiceLabels: a!forEach(
                  items: local!granteeFinancialUsers,
                  expression: rule!GAI_utilFormatUserName(usrName: fv!item)
                ),
                choiceValues: local!granteeFinancialUsers,

                value: if(
                  or(
                    a!isNullOrEmpty(
                      ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{2409b484-c88f-406c-bacf-8094aabea5c7}usernameGranteeFiscalStaff']
                    ),
                    a!isNullOrEmpty(local!granteeFinancialUsers)
                  ),
                  null,
                  if(
                    contains(
                      local!granteeFinancialUsers,
                      ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{2409b484-c88f-406c-bacf-8094aabea5c7}usernameGranteeFiscalStaff']
                    ),
                    ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{2409b484-c88f-406c-bacf-8094aabea5c7}usernameGranteeFiscalStaff'],
                    null
                  )
                ),
                saveInto: ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{2409b484-c88f-406c-bacf-8094aabea5c7}usernameGranteeFiscalStaff'],
                required: true(),
                requiredMessage: "no"
                
              )
            }
          ),
          a!gridRowLayout(
            contents: {
              a!textField(
                value: "Grantee Authorized Official",
                readOnly: true(),
                
              ),
              a!textField(
                showWhen: rule!SCO_isBoolNotEmptyAndTrue(ri!hasUserClickedGeneratePdf),
                readOnly: true,
                label: rule!GAI_utilFormatUserName(
                  ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{ce32e7a4-2cc9-4a47-8f91-2f80f075469a}usernameGranteeAuthOfficial']
                )
              ),
              a!dropdownField(
                showWhen: rule!SCO_isBoolBlankOrEmptyOrFalse(ri!hasUserClickedGeneratePdf),
                placeholder: "---Select a value ---",
                choiceLabels: a!forEach(
                  items: local!granteeAuthOfficials,
                  expression: rule!GAI_utilFormatUserName(usrName: fv!item)
                ),
                choiceValues: local!granteeAuthOfficials,

                value: if(
                  or(
                    a!isNullOrEmpty(
                      ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{ce32e7a4-2cc9-4a47-8f91-2f80f075469a}usernameGranteeAuthOfficial']
                    ),
                    a!isNullOrEmpty(local!granteeAuthOfficials)
                  ),
                  null,
                  if(
                    contains(
                      local!granteeAuthOfficials,
                      ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{ce32e7a4-2cc9-4a47-8f91-2f80f075469a}usernameGranteeAuthOfficial']
                    ),
                    ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{ce32e7a4-2cc9-4a47-8f91-2f80f075469a}usernameGranteeAuthOfficial'],
                    null
                  )
                ),
                saveInto: ri!applnProjectInfo['recordType!{ba1b9bf5-818d-401c-b540-67788e6d7d2d}GAI Application Project Info.fields.{ce32e7a4-2cc9-4a47-8f91-2f80f075469a}usernameGranteeAuthOfficial'],
                required: true(),
                
              )
            }
          )
        },
        shadeAlternateRows: true
      ),