Suddenly, pages_messaging_subscriptions permission is required
<p>I have a simple message bot that was set up according to the Messenger Platform guide.  It has been working fine for the last few months, with about half a dozen messages sent a day. I have not touched it at all, but suddenly, sending a message, ie calling <code>https://graph.facebook.com/v2.6/me/messages?access_token=...</code>, returns:</p>

<blockquote>
  <p>{"message":"(#230) Requires pages_messaging_subscriptions permission to manage the object","type":"OAuthException","code":230,"fbtrace_id":"DVs...."}</p>
</blockquote>

<p>This was out of the blue. Things were working fine, I did not even log on to Facebook during this time, and I haven't even looked at my webhook callback website.  But some time from Aug 17 onward, this exception was returned for every attempted message send.</p>

<p>Has something changed?  Anyway, I could not find a subscription field by the name <code>pages_messaging_subscriptions</code> in the Webhooks Page Subscription page.</p>

<p>What do I need to get my message bot to work again?</p>