Create Custom IDs

[YIK3S]

I want to create an ID that contains the area code the user is from, user selects their area code in the app sheet along with sequential numbers. So as an entry is submitted the numbers increase by 1 and the area code changes based on what the user has selected.
For example:

MS, AM, WW are area codes that are based on the user selection
MS0001
AM0002
MS0003
WW0004
WW0005

Please let me know how this can be done

[SkrOYC]

First of all, I would like to say that maybe this is not needed at all.
Also, ID/Keys are better just the random UNIQUEID() to make sure there aren’t any problems in the future since it needs to be unique.
You could have another field in your table that serve the purpose of this “showable ID” while not being the key for the row.
Anyway, if you want to do it agains all advice:

help.appsheet.com

Sequential Keys

A technical rationale for why AppSheet can't support sequential keys.

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What is a Key?

Learn the purpose of keys and why they’re necessary.

Serial Numbers, If You Must Tips & Tricks 💡

Danger Ahead! In general, sequential numeric identifiers (i.e., serial numbers) are risky in AppSheet: if two users happen to add rows at the same time, both rows could be assigned the same serial number, which could lead to confusion (at the least) or data loss (at the worst). For this reason, serial numbers are strongly discouraged! Basic Serial Numbers One way to implement serial numbers is with a normal (not virtual) column named (e.g.) Serial of type Number and an Initial value expression …