I vote for IB(Interactive Brokers). I’ve used them in the past as was quite happy. Pinnacle Capital Markets trading also has an API (pcmtrading.com) but I haven’t used them. Interactive Brokers: https://www.interactivebrokers.com/en/?f=%2Fen%2Fsoftware%2Fibapi.php Pinnacle Capital Markets: http://www.pcmtrading.com/es/technology/api.html
Update 2021 (Only for variable products with 1 dropdown) – thanks to @Alex Banks Anyway this will really work when there is ONLY ONE dropdown select field (so one attribute for the variations). With multiple attributes (so multiple dropdown select fields) it displays something that can be wrong depending on the variations stock status attributes … Read more
Last update: 04/22 – Tested in WordPress 5.9.2 & WooCommerce 6.3.1 Code goes in functions.php file of the active child theme (or active theme). Use woocommerce_product_stock_status_options instead of woocommerce_product_options_stock_status. This way you can immediately add a status instead of replace the existing dropdown Also use woocommerce_get_availability_text & woocommerce_get_availability_class opposite woocommerce_get_availability. This way you don’t have … Read more