Having trouble with "MIssing security rules on a related record type"

I'm going through the Appian Developer training course, following along with the exercises layed out, however today I encounter the following error when I try to allow users who can view the related records.

Missing security rules on the related record type. This rule cannot be applied because the related record type for the selected relationship does not have any security rules configured, or it uses a security expression.

I don't believe I've done anything that the exercises didn't instruct, so I'm not sure how I got this error or how to resolve.  Any help is appreciated.  Thank you!

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