Shopify B2B has a PO field but blank or invalid values can still become orders. B2B PO Guard uses a Checkout Validation Function to block bad POs before checkout completes. Requires Shopify Plus with B2B and the Online Store channel. Enable Require PO in the app, then activate B2B PO Guard under Settings → Checkout → Checkout rules. Retail stays unchanged unless you opt in.

• Require PO on B2B (company) checkouts
• Optional format rules: prefix, length, regex, presets (SAP / US Gov style)
• Store validated PO on the order (metafield + admin visibility)