Thank you @Ealfardan, it solves my problem. I will use this method.
By the way, do you know other ways of not using theme but still view the Customer Code or any fields in invoice or sales order?
I’m aware that custom theme is our own risk, so better have other safe option.
That depends on where you want to view the codes. You can include them in customer names. You can put them into custom fields designated to show on the relevant transaction forms. Etc.
@Juta, you have taken this topic too far from its original subject. That violates the rules of the forum. Your original question was marked as having a solution. So I will make one last comment, but then close this topic. If you want to continue discussion of the new issue, start a new topic.
As for showing the customer name, I simply meant to literally include it in the customer Name field.