I shared a shift with my friend who was already active on the platform. Am I eligible for the bonus?

No, only new signups are eligible for referral bonuses. Unfortunately since your friend had already signed up for the platform, the bonus isn't applicable.

How is a share-a-shift referral different from a normal referral?

In essence, they're the same. Referral rewards, expiration dates and working requirements are subject to the same terms as standard referrals.

In fact, your referral does not need to work the specific shift you shared to earn the referral reward. To qualify, they can complete any shift(s) before the associated referral campaign expires.