Set minimum per shipping method or payment gateway

@vincent14000,
Sorry for the delay in the response,
You can do it with the help of the filter ‘ct_mpac_filter_min_cart_total’ refer the following code,

add_filter('ct_mpac_filter_min_cart_total', 'filterMinimumPurchaseAmountByShipping', 12, 2);

if(!function_exists('filterMinimumPurchaseAmountByShipping')) {
	function filterMinimumPurchaseAmountByShipping($minimumPurchase, $wcCart) {
		$selectedShippingMethod = WC()->session->get( 'chosen_shipping_methods' );
		if(!empty($selectedShippingMethod)) {
			if($selectedShippingMethod[0]=='flat_rate:3') {
				$minimumPurchase = 500;
			}
		}

		return $minimumPurchase;
	}
 }