Hi, newbie here

Anyways, I've been trying to send an email on Hikki's WEBSITE i.e. https://www.emimusic.jp/hikki/index_e.php
And basically I wrote a fairly long message (about 1 maybe 1.25 pages) and when I clicked send a prompt came up saying 「郵便番号」の書式が正しくありません (roughly translated as "Zip" format is not valid)
I have no idea how that can be so I was wondering if anybody knows how to solve this problem
Is there a text limit or something that I exceeded or is it something else?

Thanks in advance