Looking for logging into the Imessage site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Imessage site. After that you can login as usual with your login credentials.
https://support.apple.com/de-de/HT204408
https://support.apple.com/de-de/HT204053
https://support.apple.com/de-de/explore/messages
https://forums.macrumors.com/threads/imessage-login-message.2113931/
https://www.imore.com/how-fix-imessage-and-facetime-activation-issues-macos
https://www.imore.com/how-set-messages-your-mac
https://telekomhilft.telekom.de/t5/Telefonie-Daten/Aktivierung-von-iMessage-und-FaceTime-schlaegt-fehl/td-p/3052461
https://www.macuser.de/threads/anmeldung-bei-imessage-fehlgeschlagen.681680/
https://appuals.com/how-to-get-imessage-on-your-pc/
https://smallbusiness.chron.com/iphone-wont-connect-imessage-66924.html
https://www.mactechnews.de/forum/discussion/iMessage-am-Mac-laesst-sich-nicht-mehr-aktivieren-333603.html
https://www.macuser.de/threads/imessage-und-facetime-keine-anmeldung-moeglich.747873/
https://www.saintlad.com/error-occurred-during-activation-for-imessage-or-facetime-on-mac/