Getting the idea it’s becoming the rage (8,2)
I believe the answer is:
catching on
'the idea it's becoming the rage' is the definition.
I can't tell whether this defines the answer.
'getting' is the wordplay.
I cannot really see how this works, but
'getting' could be 'catching' (catching is a kind of getting) and 'catching' is found within the answer.
The remaining letters 'on' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for catching on that I've seen is " Becoming popular".)