Customer Info and Extra Checkout Fields

I tried using some of the fields but it doesn't seem to work. For instance, I'm trying to send "maxquantity" as a field to send to the cart.

Along with my <form> tag, I'm sending:
<input type="hidden" name="maxquantity" value="15">

But it doesn't seem to send the value to the cart. I'm confused and have been trying to figure this out for the past week.

Any other example or a small tip would be of really great help and will be very much appreciated. Thank you very much once again!

ok let me try it and get back to you. thank you very very much!

Hi,

Thank you for getting back to me.

I tried sending the "Firstname" field and it worked like a charm.

However, I'm trying to post current logged in user's first name from wordpress and I'm running into an error.

Here's what I'm trying:
<input type="hidden" name="Firstname" value="<?php global $current_user; wp_get_current_user();?>
<?php echo $current_user->first_name;
?>">

And this is the error I'm running into:
Screenshot[URL=https://prnt.sc/sgbgsa ][/URL]

Can you please suggest tips to debug this?

Thank you very much!