This is potentially not a good idea for security reasons, BUT:
Is there a way for if activation fails due to the license being activated on a different machine: the client can inform the user which machine the license has been activated on.
Thanks!
Yep, that's what extra activation data is for: https://wyday.com/limelm/help/extra-data/
In general the best advice is to have product keys with only a few activations (so customer don't have to search hundreds or thousands of activations to find exactly which device is no longer used).