Yeah, this is a strange one. Coming from Versa 3 my original Fitbit bands fits on Versa 4, both the leather band and the default silicone band, but my 3rd party bands do not, including my favourite stretchy nylon band ( https://www.amazon.com/gp/product/B08KFFSHBH ). Seems they have made a minor design change that doesn't affect original bands, so officially Versa3/4 bands are similar, but in practice not.
I am waiting the situation out a bit and hope the 3rd party band makers figure this out (be sure to send them the feedback).
Hmm.. you have bought original Fitbit bands from fitbit.com that Fitbit states are compatible with Versa 4 and it still don't fit?
They are all called "24mm attach" as part of the name of the band, eg. one of these 10 bands: https://www.fitbit.com/global/no/products/accessories
Then I would complain to Fitbit and you might have a flaw in your device that needs to be replaced. For me several of these works across Versa 3 and 4 (sport and leather) but all should.
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