Hi Tobias, I reached out to our PureCloud Edge team and they shared this response...
"Tobias should use the global provisioning service or he should follow the settings outlined on the Resource Center:
https://help.mypurecloud.com/articles/phone-provisioning-dhcp-dns/
Create two Host A records with the same name on your DNS server:
PureCloudEdge – Primary Edge IP Address
PureCloudEdge – Backup Edge IP Address"
I hope this helps.