notification email is not working

Dear,

My client has a problem on her website https://mdnails-beauty.be.
As people are submitting for a workshop, she doesn’t receive any notification emails. So she doesn’t know when or who is registrated for upcoming workshops. And that’s of course a big issue.

Could you please help me with this problem?

Thank you so much for your swift reply!

Best regards,
B.

The page I need help with: [log in to see the link]