purchase URL validation - query parameters

Please add some additional URL validation for the product purchase path so it wont be easy to "manipulate" query parameters in the URL:

Example: quantity = 100000 in the query parameter

/checkout/?fluent_cart_instant_checkout=20&quantity=100000

ps. &quantity=-1 negative values doesnt work 😉 - I think some validation is done once the button is clicked but just highlighting

ps2. when adding minus sign to the productID: /?fluent_cart_instant_checkout=-20&quantity=-100000 we can invoke a fatal error:

Fatal error: Uncaught Error: Call to undefined method WP_Error::update() in /wp-content/plugins/fluent-cart/app/Helpers/CartCheckoutHelper.php:123 Stack trace: #0 /wp-content/plugins/fluent-cart/app/Helpers/CartCheckoutHelper.php(52):....