If you are trying to send a message to any Facebook user and facing an error, we might have an explanation here. Even if someone has interacted with your page, and when you try to send them a message, Facebook gives you an error sometimes.
Before reading about these errors, please check if your Facebook profile is connected to Statusbrew and doesn't need authentication. Read: Best Practices For Keeping Social Profiles Linked To Statusbrew
Error 01:
Facebook error: (#551) This person isn't available right now. (code 551, subcode 1545041)
Solution:
Generally, this means the user has opted out of receiving any communication from your brand page on Facebook. Facebook does not disclose any further information about this error.
Error 02:
Facebook error: (#230) Permissions disallow message to user.
Solution:
If a Facebook user has blocked Statusbrew in the Apps Platform, you might not be allowed to send them a message from Engage. There is hardly any chance of this happening with you, but if it does, the workaround is to message them via the Facebook website/app.