SellUp is designed to work with most Shopify themes out of the box. If you have checked settings and it should be showing but isn’t, you may have a custom theme or conflict with another App.
Make sure you have checked all SellUp settings and that the “Global” SellUp button is enabled as well as the individual offer’s visibility setting.
If you can’t get SellUp to show, you can manually insert the Script code in to your theme. If you are comfortable editing your Theme’s code, you can follow this article. This is usually for issues surrounding “On Page Upsells”
For issues surrounding “Action Upsells”, check out this article.
For merchants on the SellUp Pro plan, we offer a free installation assistance. Simply get in touch to arrange this.