No idea how to explain it.
If a player buys a developer product and they want to change their licence plate. When they pay for it how will the server know what they wanted to change it to?
Player enters - LICENCE123
Player buys dev product
How will server know that the player wanted licence to be LICENCE123?
Well, it's quite basic. Just have an identifier or a table.
local IDs = { [ProductId] = "LICENSE123"; [ProductId] = "LICENSE345"; };
Etc,.