By HomePlug, do you mean that I must first have a host station from Devolo, i.e. this WiFi mini only works with one host or not just this one alone?

Unfortunately I saw it too late. I just fell for it too. The device is only compatible with other DEVOLO Magic devices. According to DEVOLO support, it does not work with older DEVOLO 5550 or 1200 devices.

The above finding is described in detail in the descriptions from digitec and Devolo. So where is the problem?