Been using this for over a year and never had an issues. I've used it with Zwift and Rouvy on AppleTV, MapMyFitness/Wahoo/Solos/Strava (when they used BlueTooth) on my phone.
$25.99

https://www.amazon.com/CooSpo-Fitness-Tracker-Waterproof-Bluetooth/dp/B07BSDY2R2/ref=sr_1_8?crid=2EYMBVNLZSDY0&dchild=1&keywords=heart+rate+monitor&qid=1582050678&refinements=p_36%3A1253556011&rnid=386589011&s=sports-and-fitness&sprefix=heart+rate+%2Caps%2C176&sr=1-8