OP, is it there is no hidden extra conditions? Ok, they aren't asking for KYC. But as I read on their website, you and your affiliate will receive free £5 only after making first transaction. It means that you have to deposit money to Curve in order to get bonus.
Source - https://support.imaginecurve.com/hc/en-gb/articles/360000281165-How-do-I-refer-friends-?mobile_site=true