Explanation of the error: In order to be able to support multiple discounts POS system needs to use modifiers with serial numbers. POS shows that error message when it detects luck of support for that functionality. That is controlled by the Punchh dashboard.
Punchh dashboard is not set up to use modifiers.
Punchh dashboard is not set to support modifiers for the business and
POS needs to support multiple discounts
POS is able to detect that situation
Enable checkbox “Include Modifiers with base item” in the Punchh Dashboard=>Settings=>Line Item Selectors