How to migrate from V2 to V3 without new api keys

We would like to migrate our Uptrends Pagerduty integration to V3. Its not clear on how to do this from

  1. It seems to imply we have to create a new api key but this is not a option for us as this would mean we would have to ask all our clients to generate new api keys.
  2. Its not clear what the differences are between V2 and V3. What do we need to change in our code to make it work with V3 or can we use the same code we used for V2 for V3 as well?