Can't create transform rule on some domains, same rule works on others

I’m creating a transform rule equaling the following expression:

(http.request.uri eq "/.well-known/apple-developer-merchantid-domain-association.txt")

To (static) rewrite it to the file in a subfolder. This works on all of my domains except one. All are on the free plan.

The error on the one domain is:

not entitled: the use of operator Matches is not allowed, a Business plan or a WAF Advanced plan is required 

I don’t understand why I’m getting this error on only one domain, they’re all on the free plan.