This is the one I bought. It fits like the larger band that comes with the HRM:
FITCENT Replacement Armband Strap... https://www.amazon.com/dp/B0B31PG3MP?ref=ppx_pop_mob_ap_share
Yep. Here’s the one I have. Can’t tell a difference from the one it came with. FITCENT Replacement Armband Strap... https://www.amazon.com/dp/B0B31PG3MP?ref=ppx_pop_mob_ap_share