Minimum Purchase Quantity per Product

$wpide_min_qty = array(
    'minimum'     => 2,       // Minimum units per product.
    'product_ids' => array(), // Limit to these product IDs, empty for all.
);

$wpide_min_qty_applies = function ( $product_id ) use ( $wpide_min_qty ) {
    return empty( $wpide_min_qty['product_ids'] ) || in_array( (int) $product_id, array_map( 'intval', $wpide_min_qty['product_ids'] ), true );
};

add_filter( 'woocommerce_quantity_input_args', function ( $args, $product ) use ( $wpide_min_qty, $wpide_min_qty_applies ) {
    $id = $product->get_parent_id() ? $product->get_parent_id() : $product->get_id();

    if ( $product->is_sold_individually() || ! $wpide_min_qty_applies( $id ) ) {
        return $args;
    }

    $args['min_value'] = $wpide_min_qty['minimum'];

    if ( ! is_cart() && (int) $args['input_value'] < $wpide_min_qty['minimum'] ) {
        $args['input_value'] = $wpide_min_qty['minimum'];
    }

    return $args;
}, 10, 2 );

add_action( 'woocommerce_check_cart_items', function () use ( $wpide_min_qty, $wpide_min_qty_applies ) {
    foreach ( WC()->cart->get_cart() as $item ) {
        $product = $item['data'];

        if ( $product->is_sold_individually() || ! $wpide_min_qty_applies( $item['product_id'] ) ) {
            continue;
        }

        if ( (int) $item['quantity'] < $wpide_min_qty['minimum'] ) {
            wc_add_notice( sprintf( 'Please order at least %1$d of "%2$s".', $wpide_min_qty['minimum'], $product->get_name() ), 'error' );
        }
    }
} );