It should be set to full or unlimited.
The button Add Adjustment is displayed based on the combination of the profile “OM: Discounting Privileges” and the “enforce List price” flag for the Order Type. If the order type is not entered then we do not consider the “Enforce List Price” flag and assume it to be false. We look at the profile OM: Discounting Privilege to see if the user has the privilege to apply the manual adjustments. Also if this privilege is FULL, then if the Order Type has Enforce List Price, a manual adjustment cannot be applied. If the privilege is None the user can never apply a manual adjustment. If the profile is