Assigns one or more customers to an existing customer program.

If a customer is already assigned, the assignment will be updated.

Important considerations

• program_code is required and must exist in the database.
• The program must be active—customers cannot be assigned to inactive programs.
• customer_ids array cannot be empty.
• Non-existent customer IDs are automatically filtered out; only valid customers are assigned.
• If all provided customer IDs are invalid, the operation fails.
• For customers already assigned to the program, their old assignment is deactivated and a new one is created.
• The response distinguishes between newly assigned customers and updated assignments.
• Supports bulk assignment, multiple customers can be assigned in a single request.
• All operations are atomic, if any step fails, no assignments are made.
• Customer existence is validated before assignment to prevent orphaned records.