In some circumstances we need to clarify the compatibility of an extension with Flarum. Eg the current premium extension backup is only available for the upcoming 0.1.0-beta.8 of Flarum. It is listed as extension, but will fail to download for two reasons; being premium and not being compatible with beta 7.
Aside from showing a compatibility table in the extension view page, it would be wise to show a clear warning when extensions are only available from upcoming releases on.