iPad Pro 11" + iPhone 15 Pro Max + 2degrees 4tw!
These comments are my own and do not represent the opinions of 2degrees.
To elaborate on what saltyNZ said, 2deg on the default "internet" APN no longer give out public IP addresses, instead you get a private IP in the 100.x.x.x range and they do NAT to translate that to a real IP address.
This will very likely be the cause of your VPN breakage.
You could use the "direct" APN which would give you a real IP address, but it will also not be firewalled so you could potentially be billed for data you didn't initiate.
I'd really like to see 2d offer a compromise here. Maybe paymonthly users get a real IP and prepay get NAT? Or another APN we can use. NAT is a pain.