Metalink Note (this is deailing with AP transactions only)
From Metalink, article ‘‘
The issue has been analyzed on Bug.8418407: R12 CUSTOMER TAXPAYER ID FIELD ON INVOICE WORKBENCH, USAGE AND PURPOSE
Per R12 design the operating unit and legal entity do not hold one-to-one relationship anymore, which is in sharp contrast to 11i. Now one operating unit can be attached to many legal entities in a ledger. Under General Ledger (GL) responsibility, Setup : Financials : Accounting Setup Manager, all the legal entities of a primary ledger or secondary ledger can be found.
Here, customer refers to the Apps deploying agency that is liable to pay a supplier invoice and is accountable to legal authorities for it. So once the “customer taxpayer id” is selected at the header then the system doesn’t default legal entity on the basis of “bill to location” of the selected supplier site and the invoice liability account. The “customer taxpayer id” gives a way to explicitly override the default legal entity derived from supplier site and liability account and default org id. “Customer taxpayer id” is the unique reg. number used to identify an LE. Also “Customer Taxpayer ID” can be used for any type of invoices. The system does not consider it to be mandatory.
In summary, the customer taxpayer id is used to explicitly override the default legal entity derived from supplier site. On the contrary, the taxpayer id is used to enter tax information about the individual or legal entity, which can be a corporation or a partnership.
So the Legal entity that is chosen is first determined by the balancing segment value that is linked to the liability account and then the legal entity that has that balancing segment associated to it is chosen. You can then mnually change this by choosing the value in the ‘Customer Tax Payer ID’
How does this affect ebtax?
You can link the tax regime to either the OU or the LE and therefore use this as the way for driving the tax for your AP transaction. Ideally, you will have a solutoin where there is only one LE linked to your OU and in this case youc an only ever choose one value for the customer tax payer ID so you would never have to choose it as it will be the default. But if you do have more than one LE linked to your OU then you can only determine the place of supply for the tax regime rules with the bill to or ship to. As there could be multiple ship to values then it the only other approach is to change the bill to and to do this you need to change the legal entity (customer tax payer ID).