I forgot. With that firmware version, I have not managed to pair my band 6 without having my fit installed. When I try to pair it with the authentication key, the bracelet tells me to update the app .. we may have to wait for Notify for Mi Band updates or downgrade to supported firmware version.
Hi, exactly the same thing happened to me yesterday, I thought I had briked it.
Yo need download and install modified mi fit all in one 5.3.0 app, this recognize your smart band and you will be able to pair and repair your firmware and update from there.
sorry for my bad english.
A greeting!