In Germany many sockets are of the protective-contact type (Schuko). Unlike some other countries, where a third hole is provided for earthing, Schuko sockets earth via side contacts, the so-called protective earth contacts.

This means the grounding sheet still works correctly, because it is connected to the socket's protective earth conductor and the earthing is carried through those side contacts. No additional «third hole» is required.

Feel free to send us a photo of the socket so we can narrow it down. The most important thing is always that the socket was installed by a qualified electrician.