old question, but might help someone. For me, the problem was that if the confidentiality of messages is publicly available, then you can access it in the way you do and it works fine, but if there are user settings in the confidentiality, you will get the above error. The fix that worked for me was to get the read_stream permission from the user, if the user gives you that permission, than you can use the message just like you do (for example, [post_id] / likes)
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