Customer online appointment Booking

[AnMye]

Ive been away from using my booking site system for a year. I didn’t disable it , I just didn’t send people there anymore.

But recently I sent a guest there to book because she has canceled 4 times in the last Month and I’m tired of fooling with her. So I thought if she booked online it would save me time on my phone with her. But when she tried to book online she sent me a message saying she can’t get signed in. She said she’s getting texts saying to enter a code. 
I’ve never had a guest say they had to enter a code before. Is this something new?

How should I direct her in the future?