When you get ” this person isnt receiving messages from you right now” from Facebook it may mean either of this two scenarios.
The person you are trying to send the message to has blocked you or,
That person has deactivated his/her facebook account.
To know which of the two is true you can look at his profile picture and if its on then you are a bother to them they have blocked you. But if you see only the Facebook default photo, then this may mean that they might have deactivated their account.
It could also mean that the person you are trying to send the message has not yet accepted your friend’s request then and untill then your messages remains blocked. So if they will not accept your friend request and you try to send them a message then Facebook will not allow it rather they will send you that message.