After installing Sales Box, the Sales box section is automatically added to your current Shopify theme.
When you change a new theme, Sales Box often cannot recognize its old position. AND you have to manually update it with this link:
And if it doesn't work, please create a staff account to email: email@example.com for us to log in and add shipping box. Make sure to give us Products, Apps, and Theme access permission, then notice us on by a message. We'll check and help you asap.
Sorry, and hope this helps!
For more details on how to create a staff account, kindly read this article.