WooCommerce Checkout Field Manager validation error

I recently bought this plugin: WooCommerce Checkout Field Manager

When I activate it and fill in the checkout form to test it out, even though I filled in all the fields, I always get the error saying I didn’t fill in all the fields and I can’t proceed to the payment.

I’m using the version 4.9 of WooCommerce Checkout Field Manager.

Any help or hint would be appreciated.

Thank you.