It is the secret key you get when setting up GA or Authy.

It will be like setting up a new GA but on authy, you will need to know the 'secret'.

Is is what the exchange website calls "API key" or "key secret"?
There are 2 different keys>

I think it is key secret. API key is something else.

It should be under 2FA if the exchange has a tab for it.

Yes, the key secret is there, thanks.