In order to watch On Patrol:Live on your Roku devices, you will need to subscribe to one of the "cable-alternative services" that carries Reelz live programming.
From this Reelz link, https://www.reelz.com/extra/how-can-i-watch-on-patrol-live/, you can see that Peacock (premium and premium+), DirecTV Stream, Sling, Philo, and FreeVee are among the services. I am not actually sure how Freevee fits into the above and I didn't see it under a search.
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