Hi everyone, I'm going to tell you my history trying to pair my Ticwatch S2 to a Xiaomi phone. I had a Redmi Note 5 Pro phone so I faced for the first time that pairing issue, to get it working I changed the rom to an AOSP so it worked. Later I lost my phone and bought a Mi A3 xiaomi because it comes with Android One (kinda pure Android) so for the first time it worked like an AOSP rom, after a few time tried to pair again then It didn't pair so I needed to install a custom rom then it worked. A few months ago I started using MIUI 12 custom rom but as always It didn't connect to MIUI rom, I reinstalled stock rom to see if it pairs but it didn't work, flashed custom roms, didn't work. So I thought It won't pair, so I paired the watch to a Samsung phone because it usually used to connect successfully and as it was unused for sometime It got updated, after I reseted the watch and tried again to pair to MIUI then it passed the "Getting your watch details" screen, that was amazing to pass that screen but sadly it didn't connect at the end, but ended the pairing process successfully in the phone but didn't get the welcome screen in the watch. Now I can't continue developing my theory because I damaged the battery and I have to replace it, but I think I can give you the answer to the problem.
In my opinion the pairing problems comes because the watch can't "disconnect and reset" clearly when you failed to pair so it gets into an infinite loop that won't allow you to connect at least to a Xiaomi phone with MIUI. I'm not sure if I read something similar in another site.
- Fisrt, I would say it won't to connect to MIUI so install an AOSP rom or Android One stock.
- Second, If it doesn't pair for the first time, pair to another brand smartphone (i.e.: Samsung), when it successfully paired go to settings and "disconnect and reset".
- Third, do the clear data process in the xiaomi phone (delete Bluetooth device, google play services clear wearable, and clear data of wear os app, restart phone).
- Then, try to pair watch with xiaomi.
I hope it works for you, sadly I can't prove by myself because I killed my battery
PD: If someone knows where to buy an original battery replacement let me know.