I created a custom field for supplier invoices to add their stock code and would like to link it to my inventory using a custom field. Even though i create a custom field with exactly the same name it is not the same according to manager. Would be nice if there was a way to link it.
Custom fields apply to one subsidiary ledger (such as an inventory item) or one form (such as a purchase invoice). The only linkage that exists is when copying one form to another. If identically named custom fields exist on both forms, the content will copy.
If I understand correctly what you are trying to do, you should define a custom field for your inventory items for the supplier stock code. Set it to show as a column (if desired) and on printed documents. Whenever you buy that inventory item, the custom field will automatically appear:
The idea is that when i select to my code on purchase invoice that the supplier code from selected supplier appears as well. Some accounting/inventory apps allow you to define supplier codes for your code. Sometimes i purchase products from 2 or 3 different suppliers and each has its own code for exactly the same product.