Custom Validation using vlookup or list

[Country_Calc]

I want apply custom validation to a cell that will first check to see if a vlookup relationship exists.

If it does to return that value.

If it does not then the user has to select from a list.

I have tried to do this using IFERROR, but it does not work with these examples.

=IFERROR(VLOOKUP(A2,array_name,2,FALSE),=Lists!$A$1:$A$26
=IFERROR(VLOOKUP(A2,array_name,2,FALSE),Lists!$A$1:$A$26

 

[Country_Calc]

If the vlookup value matches a planned value on the list, then a custom formula is not needed. I can just apply a list validation with designated error value.

=IFERROR(VLOOKUP($S4,array,2,FALSE),"TBD")