Achtung: The single most common mistake, already flagged in chapter 65: the key in the layout XML's renders array doesn't exactly match PointsRedemptionConfigProvider::METHOD_CODE - no JavaScript error, no PHP exception, the method is simply missing from the list. Always check window.checkoutConfig.payment.methods via browser devtools first, to see whether the method code even shows up as available there, before looking at the renderer registration.

Achtung: collectRates() and the AvailabilityHandler check potentially run multiple times per request - any booking logic there (ledger entry, points balance reduction) would deduct again on every repeated call. The same mistake as with ApplyPointsRedemptionToTotalsPlugin (chapter 39), and the solution chapters 63/67 deliberately chose: book exclusively in sales_order_place_after, guaranteed exactly once per order.

Achtung: If AvailabilityHandler::handle() (chapter 64) throws an unhandled exception - for instance because CustomerRepositoryInterface::getById() fails for a customer that's since been deleted - the ENTIRE payment step breaks, not just this one payment method. The ValueHandlerPool catches nothing here automatically. Defensive type checks (instanceof) and early return false paths instead of deeply nested access are not a style choice here, but robustness.

Achtung: A new system.xml group (chapters 64/67) only needs bin/cache-clean config. A new database column (chapter 63's quote.loyalty_points_to_redeem) or a new data patch (chapter 63's InstallSalesLoyaltyRedeemedAttribute), however, absolutely needs bin/magento setup:upgrade. If only the cache gets cleared, the column stays invisible, and $quote->setData('loyalty_points_to_redeem', ...) either fails or gets silently dropped on save.

Achtung: payment.xml's allow_multiple_address (chapter 62) is deliberately 0 for mironsoft_loyalty_points: a multi-address order (several shipping addresses, several partial orders out of one cart) has no single, unambiguous grand_total that AvailabilityHandler (chapter 64) could check the redeemed points amount against. Leave the value at its default of 1, and the payment method shows up there without the availability logic ever having been tested for it.

Achtung: If sallowspecific/specificcountry are missing from system.xml (chapters 66/67), "Free shipping via points" can't be restricted to specific countries in the admin, even if checkAvailableShipCountries() is called correctly in code - the check simply always reads the same, non-editable default value.

Achtung: The custom Router from chapter 46 specifically intercepts the pretty URLs under /rewards/.... Controller\Ajax\ApplyPoints (chapter 63) deliberately uses the plain, technical default route mironsoft_loyalty/ajax/applypoints and needs no router change for it. Accidentally trying to "prettify" this route through the router too breaks the AJAX call from chapter 65 - form/AJAX targets aren't SEO-relevant, the same reasoning already used for the redeem form in chapter 53.