Hi,
This issue comes from the CSS of your template. It adds padding to the input so you don't get to use the full width of the input field.
If you switch to the default template, you should see that it displays without the padding and thus you can easily enter two numbers in the input field (and you don't usually purchase more than 99 elements.
So you can simply fix the issue by adding CSS to your website, in the template, or in HikaShop.
You can either force the padding to 0, or you can increase the width of the input field.
www.hikashop.com/forum/2-general-talk-ab...-quantity-field.html
www.hikashop.com/support/153-customize-the-display.html