Ah, I think I know what’s wrong here (at least I have an idea). Its a bit of a “chicken and egg” problem.
- you already have 8.7.0 installed
- when you now install the app, this in the background wants to install kopano4ucs
- kopano4ucs has the dependency on kopano-server-packages (any version)
- at time of install only the app repository with 8.6.8 is available
- kopano-server-packages has a hard dependency on packages from the same version
- so it wants to install kopano-server-packages 8.6.8, which fails since you have already something newer installed
Workaround would be to manually configure a repository that has 8.7.0 (or newer) and then install the app again.