The link doesn't work.
You need to send the link to the bundle's editing page, but only send it once the bundle is ready. If someone agrees to participate, you won't be able to edit certain aspects of the bundle afterward.
Okay, it's working now. Use one of these two links:
https://itch.io/bundle/3772/edit
https://itch.io/bundle/3772/edit#participants
Both will work the same way.