While update primary emergency contact address detail, say zip code can be updated with alphanumeric value, though only numeric value is supported for a country zipcode.
Employee Central - Emergency contact
Reproducing the Issue
No validation message is put for invalid zipcodes, the same validation works in employee address and dependents address sections.
Currently this is a design behavior as the validation part was not implemented in emergency contact part of code and engineering team is planning to implment the uniform behavior as an enhancement.
There is no fix plan yet, you can request an enhancement to push the implmentation as per KBA-2090228.
ECT-103194 , address validation emergency contact, zipcode emergency contact. , KBA , LOD-SF-EC-PER , Person Data (All Person Data Types) , Product Enhancement