Hi,
If you are sure about tolerance key setting in OMR6 t.code for your company code, then for invoice block in your case - check other two options may cause your concern
Option-1 :=> Cross check vendor code in PO and also in your invoice - Now find is there any invoice block set in field of Payment block for your vendor master in Payment transactions view in Company code data in t.code OXK3 and if set , remove for Free payment in t.code XK02, and save. Go for invoice verification. again to see the difference by creating new PO
Option-2:=>
Other option to check payment term used in your PO and in Invoice posting - Now find any Blocking key assigned in field of Block key in segment of Pmnt block/Pmnt method default segment for your payment term in t.code OME2, if yes- then remove for Free for payment and save. Go for invoice verification again to see the difference in your updated settings.
Regards,
Biju K