If you are trying to build a High Availability cluster and receiving an ‘Invalid Response from Peer’ error, as shown below, this is most likely due to the Security Keys not matching throughout the three servers:
Scroll down to Node Status on the Primary server and copy the Security Key:
Paste the Security Key into the Security Key tab for both the Auxiliary and Arbiter:
With the Security Key matching on all three servers it should be possible to form the High Availability cluster.