They only support client to server XMPP, not server to server XMPP.
Facebook Chat should be compatible with every XMPP client, but is not a full XMPP server.
So you can use any XMPP client for the Facebook Chat, but you can only chat with other Facebook users.
Which is a pity. Welcome to the 90s.
From Facebook Help Center:
When your message is delivered, it will be marked as sent. If your message fails to send, you'll see a message saying that it didn't go through and you'll have the option to send the message again.
It means your message already has been delivered.
If it's a public page and message icon is there then admin don't have to accept ...
I couldn't find the answer to this anywhere, so here you go!
Go to https://voice.google.com
Navigate to the section you want to archive (calls, messages, or voicemails)
Click on the circle icon next to the first message you want to archive. Notice that when you hover over the item, the circle changes to a gray checkmark. When you click it, it changes to a ...
You can prevent random accounts from adding you to Instagram Message Groups. This should stop most of the Group Message Requests spam.
Instagram > Settings > Privacy > Messages > Who Can Add You to Groups
NOTE: this setting is present on some accounts, not accessible on others. Your account may not be able to access this setting.
Settings > ...
Having test it myself, I conclude:
Yes, the message will only be marked as Sent even if it is successfully delivered to the page (which is almost instantly)
When the admin of the page is on their personal account, only your last message will be displayed in the notification to them
If they click on it it will be marked as Seen immediately. There is no need ...