validation

Your logic shows the message in case the user is a member of that group. Is that what you want?

yes, if the selected user is belongs to that user then show error/warning message 

OK, but what is wrong with it? What did you do to test your logic?

my logic is showing warning message to all selected users but not some particular user 

for ex: all users- abc,xyz,pqr,wtu,ijk

for users - abc,wtu when i select these users then it has to show warning message

my logic is showing warning message when i select pqr/xyz 

Hi,

you can update you logic like below

if(
    a!isUserMemberOfGroup(
    ri!approver_txt,
    cons!CR_GRP_ALL_CCC_USER_GROUP
    ),
    cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[3],
    ""
)

i have written like this but message 3 is not showing when i select ccc_user name

Isusermemberofgroup returns boolean value but here your checking with Text/user type, Don't check the value use Isusermemberofgroup alone like below.

if i make changes like that which will give me error like below

Check with below code, If it throws same error check the groups security.

if(
  not(isusernametaken(ri!approver_txt)),
  cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[2],
  if(
    ri!approver_txt = loggedInUser(),
    cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[1],
    if(
      a!isUserMemberOfGroup(
        ri!approver_txt,
        {
          cons!CR_GRP_ALL_CCC_USER_GROUP,
          cons!CR_GRP_BOARD_OF_DIRECTORS_GROUP
        }
      ),
      cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[3],
      null
    )
  )
)

Check with below code, If it throws same error check the groups security.

if(
  not(isusernametaken(ri!approver_txt)),
  cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[2],
  if(
    ri!approver_txt = loggedInUser(),
    cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[1],
    if(
      a!isUserMemberOfGroup(
        ri!approver_txt,
        {
          cons!CR_GRP_ALL_CCC_USER_GROUP,
          cons!CR_GRP_BOARD_OF_DIRECTORS_GROUP
        }
      ),
      cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[3],
      null
    )
  )
)

this logic will give this error

 if(
        isusermemberofgroup(
          ri!approver_txt,
          {
            cons!CR_GRP_BOARD_OF_DIRECTORS_GROUP
          }
        ),
        cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[3],
        if(
          isusermemberofgroup(
            ri!approver_txt,
            {
              cons!CR_APP_GRP_HOC_GROUP,
              
            }
          ),
          cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[3],
          if(
            isusermemberofgroup(
              ri!approver_txt,
              {
                cons!CR_APP_GRP_DCEO_GROUP
              }
            ),
            cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[3],
            if(
              isusermemberofgroup(
                ri!approver_txt,
                {
                  cons!CR_APP_GRP_CEO_GROUP
                }
              ),
              cons!CR_NEXT_AUTHORITY_VALIDATION_MESSAGE[3],
              null
            )
          )
        )
      )

this worked

Please note also that if you're on a reasonably modern version of Appian, you should be using the newer function a!isUserMemberOfGroups(), which automatically handles checking many groups (and built-in logic for requiring the user to be a member of all listed groups or any listed groups).