Shopify does not seem to recognise postcodes for Jersey in the typical UK format with having a space between the two groups of letters/numbers.
Users from Jersey have to include their postcodes without the space e.g. JE24YE. However this is not typical for UK postcodes, they are normally written JE2 4YE. This works for all other areas of the UK.
The images below are for a random supermarket in Jersey and not personal information.