According to AP Help -
Tax retrieval hierarchy
Tax groups and rates prefill on Accounts Payable invoices from the following locations in the following order:

1. JC Commitment record
2. JC Job
3. AP Vendor record (Setup Vendors, Terms and Defaults tab)
4. AP Settings (Invoice Settings, Tax Settings)

We don't use PJ so my suggestion may not be useful. However, it sounds like you need to leave the tax field blank on the commitment and then it would look to the AP Vendor record which seems to be working for you.

You can't override the tax group on a commitment. You may have to add additional lines to the invoice that are for the tax liability amounts only that are not linked to the commitment. (in the AP Distributions)
You may want to call support for help in determine how to make this work

I am running into a similar issue and am curious if you've found a good way to remedy this. We also have costs that need to be committed and therefore need the amounts available in the contract amount, but don't want the tax amount to show on change orders that go to the vendor. I am hoping that using the TL tax features could help with this.

I am currently trying to work with the tax liability features in AP to automatically put our invoices to our sales tax payable account, but previously we would just code the invoice header as the amount payable to the vendor and then create multiple distributions on the invoice - distribution(s) coded to the job to bill for both the amount payable to the vendor and the amount of the tax, then a distribution for the negative amount of the tax to our sales tax payable account.

Some workarounds we have found that are not exactly ideal, but can work:

- Create change orders for the tax amount on the commitment, but do not check the "revise commitment" box / leave pending. This way, future COs to the vendor reflect the actual amounts being paid direct to the vendor but there is at least some record of the tax amounts in the commitment. When you get to the end of the contract, it will look like you have a negative balance, but it is easy enough to check that all pending COs are for tax and that the pending CO amount is equal to the commitment balance overage.

- Create a second commitment for the same job and same vendor for the tax only. All change orders for this tax commitment will be internal simply to add that tax to the proper place on the budget. When coding an invoice that needs tax added, use the original commitment for coding the amount to be paid to the vendor, and use the tax commitment to bill for tax.

Note that for both of these workarounds, we did not even have the tax feature turned on, so all of these amounts were simple in the "amount" column, not in tax or tax liability.

It seems to me that for our purposes, we would either need PJ to have a "tax liab" column similar to in AP and that this amount does not increase the commitment amount. Or if there is a way to change the crystal report for commitment COs so that the amounts on the CO do not reflect tax, that would probably work too.

We are also on Sage 300 CRE 15.1 using AP, AR, CM, GL, JC, PR, PJ