More readable is using the enumeration functions (read more here: https://docs.mendix.com/refguide/enumerations-in-expressions):
Compare caption:
getCaption($Coste_Externo/Proveedor) = 'Versia'
Compare key:
getKey($Coste_Externo/Proveedor) = 'Versia'
Comparisons are Case-Sensitive. Eventually, use function toLowerCase() like so:
toLowerCase(getCaption($Coste_Externo/Proveedor)) = 'versia'
you need to put Versia with quote. Like that : ‘Versia’