In this case its pretty straight forward (although the resolution may not be) that the string which represents the users is not valid when it gets read by PAD to it fails.
Just like in Cloud flows you should add in code to do the following
--output the value of the email before you attempt to use it, when I do this in cloud i wrap the value in -- and -- in the front and back so I can see if there are any weird characters or spaces.
--the above will also show you what its attempting to use so you can tell right away if its bad
--after checking the values, make sure you do not have any spaces etc and or if you found the issue good, but this happens a lot where there trailing or end spaces or weird characters hence the request above. Use trim to make sure, but again, don't use that in the first test, just spit the value out to either a log file or Display message so you can see it.
Something is wrong with how its reading the data, or something in the data even though it looks good.
If you check the above it will show you right away.
If these suggestions help resolve your issue, Please consider Marking the answer as such and also maybe a like.
Thank you!
Sincerely, Michael Gernaey