Okay, the PayPal Payments plugin is new and we believe that the plugin is not fully compatible with WooCommerce but not sure. Could you please try with deactivate our plugin and using the WooCommerce default coupon? As we are using the default WooCommerce negative fee for partial payment.

Also, you can disable partial payment using code

add_filter('woo_wallet_disable_partial_payment', '__return_true');