Usually the cart has not reached the tier minimum, or a better price already applies and the buyer is keeping it.
Check these in order
The cart quantity has not reached the tier minimum.
Tiers are evaluated on the quantity of each line in the cart, not per order line across visits, and a collection tier does not add up quantities from different products.
A better price already applies.
Tiers never make a buyer worse off, so if a custom price already beats the tier, the buyer keeps the lower one. That is working as intended, not a fault.
A narrower scope wins.
A product tier beats a collection tier, which beats a group tier.
How to fix it
Open Customer Groups → Volume tiers for the buyer's group and use the live preview to check what the tier produces at the quantity in the cart. Lower the minimum, or remove a narrower tier that is taking precedence.
If it still is not working
Send us the order number and the customer's tag through Still stuck, and we will read the checkout function's own run log for that order.
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