Add minimum spend before postage is added

Hello,
I added a code to have a minimum spend of £20, but that seem to include postage. Is there a way to set this price before postage costs are added?

code i used is:

add_action( ‘woocommerce_checkout_process’, ‘wc_minimum_order_amount’ );
add_action( ‘woocommerce_before_cart’ , ‘wc_minimum_order_amount’ );

function wc_minimum_order_amount() {
// Set this variable to specify a minimum order value
$minimum = 20;

if ( WC()->cart->total < $minimum ) {

if( is_cart() ) {

wc_print_notice(
sprintf( ‘You must have an order with a minimum of %s to place your order, your current order total is %s.’ ,
woocommerce_price( $minimum ),
woocommerce_price( WC()->cart->total )
), ‘error’
);

} else {

wc_add_notice(
sprintf( ‘You must have an order with a minimum of %s to place your order, your current order total is %s.’ ,
woocommerce_price( $minimum ),
woocommerce_price( WC()->cart->total )
), ‘error’
);

}
}

}

Thanks
Matt