551 error with Facebook Messenger bot - "This person isn't available right now"

Question

I've written a simple bot for Facebook Messenger that takes a user's text, applies a simple transformation and immediately returns the result.

While testing it myself, I've never had a problem, but it seems that for some users, Facebook returns the following error when the transformed message is sent back (from my server logs):

"www-authenticate": "OAuth \"Facebook Platform\" \"invalid_request\" \"(#551) This person isn't available right now.\""

Any ideas what the cause of this would be? It seems to arbitrarily happen to random users, and users should be available as the result is returned immediately.

Thanks!

Answer 1

This is currently a confirmed bug on the Facebook platform. Bug location: https://developers.facebook.com/bugs/465154327166499/ (as mentioned by @m90, Facebook developer account is required to view it).

Bug description and steps to reproduce:

1. Have a new Facebook user (who never interacted with your app before)
2. With that user, ask anything that normally produces automated response from the app

Expected result: Bot should respond

Actual result: For apps in development mode it is error code 551 as following:

{"error":{"message":"(#551) This person isn't available right now.","type":"OAuthException","code":551,"error_subcode":1545041, ...

For apps in production mode (already submitted and public) it is error 200 as following:

{"error":{"message":"(#200) This person isn't available right now.","type":"OAuthException","code":200,"error_subcode":1545041,...

Note: if the user sends more messages, bot starts to reply normally after the 2nd message from the same user.

Based on the information from the Facebook Platform bug page, the bug has appeared in the end of May 2017. On our side, we have been noticing this for the last week (since around June 5), important to note that new app submissions are also failing because of this issue.

UPDATE June 09, 2017 Bug is marked as fixed and works on our side now. If you still experience issues, Facebook asks to comment on the bug page.

Answer 2

I got the same error, It was due to the fact that my page was unpublished. Once I published the Facebook Page this error was gone.