Hello homan374 -
As long as the scrolling gallery is enabled in your account preferences and you have a valid token linking to your eBay account, the scrolling gallery should append for you automatically and operate as expected.
If your account has a valid token and the gallery is not operating for you as expected, please feel free to file a support case from under the Help tab of the site letting our agents know the trouble you are experiencing and please include a few item numbers for where the gallery is not displaying as expected so we can look into it for you.
- Craig