The app automatic location placement does work with Gempages, however the location can sometimes be hidden or only showing on desktop/mobile.
In this case you can setup a custom location for the upload on the Gempages template.
In the Gempages editor add a new element of the "Liquid":
Drag the Element to your desired location.
Side note: It most cases it is recommended to add the element inside a "Row" element.
Enter a name for the element:
Edit the Liquid element:
Copy & paste the following template:
Save the template.
Inside the Upload-Lift app, set the location to "Custom":
Enter the following selector:
Save the upload field. The field should now appear on your product page.