Minimum Order per Shipping Method only

I am trying to fix a minimum order based on the shipping method “flat rate” (as below) but it is not working:

// Set the minimum order amount, shipping method before checking out
$minimum = 50000;
$shipping_method = ‘flat_rate’;

// Defining var total amount
$cart_tot_order = WC()->cart->total;

// Compare values and add an error in Cart’s total amount
// happens to be less than the minimum required before checking out.
// Will display a message along the lines

if( $cart_tot_order < $minimum && in_array( WC()->customer->get_shipping_method(), $shipping_method ) ) {
// Display error message
wc_add_notice( sprintf( ‘A Minimum order of LBP%s is required before checking out.’
. ‘Current order: LBP%s.’,
$minimum,
$cart_tot_order ),
‘error’ );
}
}

Any ideas about the reason?