Checkout page not working correctly?
By default, PGS Woo API plugin create app checkout page.
Here we can see on Admin pages listing.
Make sure app checkout page has WooCommerce checkout page shortcode [woocommerce_checkout]
If ( W3 Total Cache ) Total Cache Plugin is enabled on your site please follow below steps for app checkout page.
Step 1 Go to the Performance->Page cache.
Step 2 find Never cache the following pages:
Step 3 add checkout page slug here /app-checkout/