#_PAYMENT_URL broken

We have an event with the booking recorded email for that event set up this way:
–snip–
Dear #_RESPNAME,

You have successfully reserved #_RESPSPACES space(s) for #_EVENTNAME.

Please remember to submit your payment through PayPal at #_PAYMENT_URL.

Best,
#_CONTACTPERSON
–snip–
However, the URL that is returned in the email leads to a 404 error.

This is the third year we’ve run this even using EME with PayPal, so I doubt it’s an error setting up the event.

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