My addon Can I Mog It? does not show up in the Curse Client as installed or via search nor does it allow you to install it using the "Install via Curse Client" button on the website. The Downloads window opens, but it's just white.
The addon was originally experimental and I think uploaded by hand but has since been only pushed using Git.
I've tried downloading different addons and they work perfectly fine.
I've tried with two different computers, two different accounts, logged in and logged out, and it still doesn't work.
Thank you very much for your help Torhal. Posting solution here too in case it comes up again.
Solution: The file needed to be tagged for current game version to show in the client. Set the file on CurseForge to work for Live too (so 6.2.4 and 7.0.3) and it worked with the Client. Being set to 7.0.3 only meant that it wouldn't show up in the client until patch day when the version of the game updated.