shopify won't allow my customers to add more than one item to their cart

Topic summary

A merchant is experiencing a critical cart functionality issue where customers are unable to add more than one item to their cart when using Shopify or Shop Pay. This prevents customers from completing multi-item purchases, effectively blocking normal checkout operations. The issue appears to be related to the POS order management system based on the discussion tags. No resolution or troubleshooting steps have been mentioned yet, and the problem remains unresolved.

Summarized with AI on November 14. AI used: claude-sonnet-4-5-20250929.

shopify / shop pay won’t allow my customers to add more than one item to their cart