If you previously uninstall the app and then reinstalled it. You should check the app proxy to ensure it pointed to the app properly
To do that, on the Shopify admin backend, go to the apps page to see all installed apps on your store. Find 'Customify - Product Customizer'.
Then click the ‘view details’ link.
On the App Details Popup. Scroll down to find: ‘EDIT PROXY URL.’
Please ensure that the value entered in the textbox field highlight above is: ‘customify'