Trying to find a way to connect a raspberry Pi 4 with Garmin watch to send simple data files.

All you can do with CIQ BLE is exchange messages, not files.  In CIQ you can't access files, and even if you could you'd have to send the files in pieces..

For sending data, makeWebRequest calls may be easier.

Thank you jim_m_58 for you quick response. We are trying to record HRV using the watch's HR sensor, then if we can continuously feed that data directly to the raspberry pi for storage. We are able to obtain 10 secs of HRV data with an app we created but are having a hard time making the connection to the pi and sending it through. What would the easiest way to do this, would it be possible through a phone with connect IQ installed or even better just through the pi and watch.

As I said, you can use makeWebRequest calls to push the data through the phone to a web server on the pi (but you must have a proper certificate and use https.

You could use BluetoothLowEnergy as write to a specific characteristic on the pi. You'd have to build your own app for the pi.

Some of it depends on how well you understand BLE.  My pi apps are mainly node.js, 

I'm working on a related (I think) project and would love to hear what you have learned.

I have a Pi reading data from an air quality sensor and want to use it while biking and running. It can send data to ThingsBoard.cloud using MQTT via my phone hot spot. It needs location data so I can find where the good and bad air places were after a workout. It would also be great to display the air quality on my watch.

github.com/.../air-pms7003

So, ideally I need two way messages, send the air quality to the watch and send the GPS location to the Pi.

It looks like you only need HRV data messages to the Pi and could record them there (?), no need to record anything on the watch. I would love to know how you are progressing and what you have learned. I am just starting with CIQ and am going through jim_m_58's posts now.

You can do that with BLE.  In the garage do example there, I read the current state of a garage door, and send the command to open/close it.

In my current (non published version), I read a temperature sensor attached to the pi and also request that data.in CIQ.

Thanks Jim!