One Page checkout plugin with custom checkout fields

Hi there

I am using the Woocommerce One Page Checkout Plugin: https://woocommerce.com/products/woocommerce-one-page-checkout/

I would like to use the methods listed here https://docs.woocommerce.com/document/tutorial-customising-checkout-fields-using-actions-and-filters/ to add a new hidden field to the checkout.

But i don’t see it in the code of the one page checkout page: https://www.myhebrewbooks.com/4-minim-aish-la/

Does anyone know if this is compatible (support at Woo has been pretty bad… I have an open ticket on this… maybe you guys can help)

Thanks

https://www.ads-software.com/plugins/woocommerce/