Most times while filling an online form for business, scholarships etc, there is always a column for a country Zip code.
Most countries uses postal code for mailing/delivery purposes including Nigeria but Zip code (Zone Improvement Plan) code is only used by the United States of America for their mailing/delivery purposes.
According to the United States Postal Services, Nigerian Zip code is 00176 or 00176-0000
Some sites might accept codes like 23401 or 110001.
I believe this will help you when situations like this arises. Please don’t make the mistake of using 234, it’s simply the Nigerian International Phone Dialling Code.