2026-04-13 – version 5.5.4
* Fix – Correct large envelope (flat) classification to match USPS standards — items that exceed any (previously all) of letter dimension now qualify as flats.
* Fix – Legacy API credential validation no longer runs when switching to REST API, preventing headers-already-sent warnings.
* Fix – Validate empty Origin Postcode: show admin notice on save and skip API requests.
* Fix – FCPIS rates incorrectly filtered for valid custom boxes.
* Tweak – Hide product-level “Envelope” checkbox when REST API is active, as it only affects Legacy (SOAP) API rates.
* Tweak – WooCommerce 10.7 Compatibility.
2026-03-30 – version 5.5.3