Unfortunately JSON::true and JSON::false are not in its @EXPORTS yet are part of its official interface, which Subroutines::ProhibitCallsToUnexportedSubs is not happy about.
Is this JSON or ProhibitCallsToUnexportedSubs problem? eh, not here to make a case for that. Should $JSON:: versions be used instead? probably, but it's not the whats presented in the pod.
It would be useful for this policy to have an exempt_subs option like it's sibling ProhibitCallsToUndeclaredSubs or perhaps ignore_modules option like it's other sibling RequireExplicitInclusion. This would mean deciding more or less just ignoring the problem and moving forward.
Im happy to submit a PR but dont want to spend any time on it if it will be rejected