We travelled to Munich in July 2023. We understood the Umweltzone (green zone) was within the R2 ringroad so we parked outside. When leaving in the direction of Austria, we took the R2. We saw the Umweltzone plates, but assumed they warned about the Umweltzone within the ring. We also saw a "plakat" mentioning that the Umweltzone was within the ringroad. So we drove on and then exited the R2 by taking the highway exit.
We googled afterwards and apparently since February of this year (2023) the ringroad R2 itself is also part of the Umweltzone. Lesson learned: never rely on third party info.
Anyway: we didn't get stopped but we did see unmanned cameras. Is there anything we can/should do? In our country of origin you can get a post hoc permission if you accidently drove through the low emission zone.
I understand we can only order a sticker for future use. Is that right?