We are using SharePoint 2013.

We have two lists in our site: one custom list and one calendar list.

We are trying to add lookup column in Calendar list and referencing the custom list.

Adding lookup works fine. But when we tried to Enforce relationship behavior to Cascade delete, it throws an error.

Error we are getting:

This lookup field cannot enforce a relationship behavior because this list contains incompatible fields.

The Goal is to delete all the calendar items which has lookup set from custom list when the corresponding item from custom list is deleted.