Your test cart and a real shopper’s cart differ in ways that are easy to miss. Work down these in order.
1. You are logged in and they are not
The single most common cause
Conditions on Customer is logged in, Customer tag, Customer total spent and Customer order count cannot pass for a guest — there is no customer record to read. Most checkout traffic on most stores is guests, so a rule gated on any of these applies to a small minority.
Test in a private window to see what a guest sees.
2. Different destination
Shipping country is where the order is going; Customer country comes from the customer’s own address. They differ on gifts and business shipments.
Your test address is probably domestic. Theirs may not be.
3. Different currency
On a multi-currency store, threshold conditions evaluate in the cart’s currency. A Cart subtotal ≥ 500 rule fires at 500 units of whatever the customer is shopping in.
Add a Cart currency condition, or build one rule per market.
4. Different cart contents
Product conditions match if any item qualifies. A cart mixing qualifying and non-qualifying products still matches — which is right for “contains something fragile” and wrong for “is entirely digital”.
5. Different device
Express buttons are device-dependent. Apple Pay only renders on Apple devices in Safari, so testing from Windows shows it missing whether your rule works or not.
Reproducing it
Ask for: the destination country, whether they were signed in, roughly what was in the cart, and the currency shown. Rebuild that cart in a private window and the cause is usually obvious within a minute.