If you want to apply conditional validation on 'Second Country Longitude' or 'Third Country Longitude', then you need to add 'Continent' input as 'Asia'.
{{countryForm.controls?.continent?.errors?.longitude.message}}
If you want to apply conditional validation on 'Third Country Longitude' then you need to add 'Continent' input as 'Asia'.
Conditional Expression with type 'string'
{{countryForm.controls?.thirdCountryLongitude?.errors?.longitude.message}}