hier is what I have found:
Appearance of agreement means that for two parties to be considered in agreement, all that's needed is for a so-called reasonable bystander to believe that one party has accepted the offer of the other party. A court then will consider the parties as being in agreement, even though some details were never fully resolved. There's more to it than that, but this is the gist of it.
based on the above I would say:
äußerer [An]schein des Einverständnisses/der Übereinstimmung