selectively-enable-gateway.php

// This function disables the Stripe gateway everywhere except for the order-pay endpoint.  
// It also removes the Check gateway from the order-pay endpoint.

function ijab_selected_gateways_order_pay( $available_gateways ) {
    
    if ( is_checkout() && ! is_wc_endpoint_url( 'order-pay' ) ) {
        unset( $available_gateways[ 'stripe' ] );
    }

    if ( is_checkout() && is_wc_endpoint_url( 'order-pay' ) ) {
        unset( $available_gateways[ 'cheque' ] );
    }
    
    return $available_gateways;

}
add_filter( 'woocommerce_available_payment_gateways', 'ijab_selected_gateways_order_pay' );