Hi there,

As far as I know, As of the latest privacy changes, two person should
Exchange contact details in order to send / receive messages from each
other.

If you try to send a message to someone who's not in your contact;
1. In your desktop computer the messaging edit area is unreachable so first
you should send a contact request. The edit area becomes active as soon as
the person accepts your request.
2. In your mobile, if you send a message to someone who's not in your
contact, the contact request is automatically being sent and the person
should accept your request to see what message you have sent.

Regards!
Salih
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