Set a minimum order amount in WooCommerce – No Plugin used

add_action( 'woocommerce_check_cart_items', 'required_min_cart_subtotal_amount' );

function required_min_cart_subtotal_amount() {

    // HERE Set minimum cart total amount

    $minimum_amount = 250;

    // Total (before taxes and shipping charges)

    $cart_subtotal = WC()->cart->subtotal;

    // Add an error notice is cart total is less than the minimum required

    if( $cart_subtotal < $minimum_amount  ) {

        // Display an error message

        wc_add_notice( '<strong>' . sprintf( __("A minimum total purchase amount of %s is required to checkout."), wc_price($minimum_amount) ) . '</strong>', 'error' );

    }

}