F-28 tax posting error

we use F-28 to post incoming payment for company code 1110, customer account 10003, but this customer doesn't have any open item, so in "post incoming payments select open items" screen, we choose another company code 2110 and another customer 20003, 20003 has open items, we fill in the cash discount, the "not assigned" field now is zero, but when we try to save, it displays the error:

Account 3000060 2110 for deductions/discounts must not be tax-relevant

Message no. F5037

Diagnosis

The system wants to create an automatic posting for cash discount deductions or unauthorized deductions in the above-mentioned account.

In company code 2110, no tax adjustment is defined for such deductions (in table T001, it was specified that the cash discount base is the net amount). In this case, the account to be posted must not be tax-relevant.

Procedure

Correct the master record of the account mentioned above.

our setting for account 3000060 is : tax catgory:+, line item display, post auto only, since this account has balance, what should I do to save the F-28 result? thanks