It says that it can only be used on unused accounts.
https://claude.ai/referral/DWmppnEx9g?s=ios
They say I will also be given credits, but I'm sorry because I don't know the details.
I will delete it immediately if it becomes a problem.
Since the message keeps coming up, I thought it would be better to leave it alone than to just ignore it, so I'll post the link for anyone who wants to use it for a week.