Which partner function is mandatory when creating a quality notification for the Customer Complaint notification...

For a quality notification with origin "Customer Complaint" (e.g., type Q1, transaction QM01):

Sold-to Party (B): The sold-to party (customer) is mandatory because it identifies who raised the complaint, a key field in the notification header linked to SD data (SPRO > QM > Quality Notifications > Notification Creation > Define Notification Types). Without this, the notification cannot be saved.

Interested Party (A): Optional, used for additional stakeholders.

Contact Person (C): Optional, specifies a customer contact but isn’t required.

Author (D): The creator (system user) is auto-filled, not a mandatory partner function.

Thus, "Sold-to party" is the correct answer.References: SAP Help Portal - "Customer Complaint Notifications"; SAP S/4HANA QM User Guide - "Partner Functions".