Used stamps exchanges.

A.Belousov "Alexander" of Russia has sent me a cover with MY exchange ID SG-42 written . Apparently he does not know he has to write his exchange ID.
Raymond of Canada also face the same situation.
Alexander ... if you are reading this, please provide us the exchange Id RU ??? so that we can register your sending.

It seems that you have sent a letter to user sandy (http://50stamps.club/profile/sandy) and this member has sent stamps to you on your returned address. There is no letter from this member trough the system.

I have sent a private message to this member to better explain the system.

You can also contact this member to clarify this. Maybe you could consider this a direct swap?