Versa 4 vs Samsung S9 - SpO2 not working

[mobydoc]

Using Versa 4 with Samsung S9
Five days ago (Tue13Feb2024) watch was put on charge.
SpO2 readings had been working for several weeks prior to this charge.
Since this charge SpO2 has not worked.
Did factory reset on fitbit.
Uninstalled fitbit app on phone and reinstalled.
After these actions, fitbit not found when attempting to connect on Bluetooth.

Screen on fitbit shows
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Activation date: 2023_12_10 (underscores replace -)

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Add device leads to What are you setting up?
Versa 4 option selected

Fitbit Versa 4
Health and fitness smartwatch
Set up
Connect Versa 4 to the Fitbit app
You must read and accept to continue
I AGREE
Let it charge
Connect the back of your Versa to the magnetic charging cable until it snaps into place.
NEXT
Searching for Versa 4
Turn on your phone's Bluetooth, and keep your Fitbit device nearby to establish a connection.
Searching
Is your Versa 4 charging?
Make sure the display turns on when you press the side button. If nothing happens, plug it into the charger.
TRY AGAIN

At this stage pressing the side button turns on the screen 
Screen on fitbit shows
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Please advise how to proceed

[Guy_]

Hi @mobydoc - if you factory reset your watch it is like a new device.

In this case in the Fitbit App, click the device icon top left

at the bottom Add more devices and select your Versa 4, to set it up and replace [Don't add your phone].

Versa 4 and S9 SpO2 works unless you have a syncing problem with the new V4 Fitbit App.

In this case toggle Bluetooth off/on, restart the watch, logout of the Fitbit App  and restart the phone and try syncing after each step. Normally a factory reset is not required as this can complicate things.

See how that goes.

[mobydoc]

SpO2 hadn't worked for five days.
Uninstall and reinstall of Fitbit app had no effect on restarting SpO2.
Factory reset done.
Reconnect via bluetooth failed
Fitbit device not visible when attempting to connect using Bluetooth from phone.

Fitbit device not discoverable when attempting to connect using Bluetooth from laptop either.

[mobydoc]

After several hours of trying to connect via Bluetooth without success, the connection has finally been established.

Now to see if the SpO2 monitoring is working again.

[mobydoc]

SpO2 is not working 
SpO2 Signature screen showing
--%
Couldn't read SpO2

Please advise how to get this to work

[mobydoc]

The SpO2 is still not working.

Please can someone advise how can this be resolved.