Because of a Shopify platform limitation, one-click upsells only appear for shoppers paying by card or with Shop Pay - and only while the order is still editable.
Check these:
Payment method - Apple Pay, PayPal, other express wallets, and non-default currencies aren't supported by Shopify for post-purchase upsells.
Fulfilment - the order must not be fulfilled yet.
Flow rules & display conditions - the cart matches your "IF the order contains…" rule and any segment conditions.
Status - the offer is set to Live (not Test Mode or Disabled).
