Please follow these following steps to manually add this section that will display on your product page.
Go to your Online store - Theme - Find the Theme that you're using - Action - Edit Code.
Search for product.liquid file (or product-template.liquid in some cases).
At the end of page, paste this code snippet: {% include "salesbox-common" %} at the end and then remember to save.
NOTE: If it doesn't work, please feel free to contact our Support team via our live chat channel by clicking on the bottom right icon inside app, or our email at support@fireapps.io for further support.