Form button on existing web page

[roger_morris]

Hi
I am new to osCommerce and would like to add a form button from an existing web page to a product.

I am using:

<form action="/oscommerce-v4/index.php?action=cart_add" method="post">
  <input type="hidden" name="products_id" value="1">
  <input type="hidden" name="return" value="https://www.sorbaskarst.com/content/info/00006.html">
  <input type="submit" value="Add to cart">
</form>

But that results in a "The form is expired. Please go back and refresh the page" message

What am I doing wrong?