First, let's make sure you mean goto-cover and not send-calls. I apologize, I don't mean to waste your time, but this is worth confirming, so please pardon me if it's irrelevant.
goto-cover forces the calling party's call to the coverage point administered on the called party's station, for example, when the calling party doesn't wish to wait for the called party (an inside user) to answer.
Conversely, send-calls is used by the called party to send the calling party to coverage (i.e. voice mail), when the called party doesn't wish to answer the call in person.
This means that pressing the goto-cover button will do nothing, unless you're actively calling another inside user with a coverage path assigned to their station.
If goto-cover doesn't work in this scenario, then I would expect that normal coverage for the same called party wouldn't work either - try calling the same number and see if it goes to cover normally - and you should troubleshoot the individual station, coverage point if a path has been administered, or device or service that the path is routing to.