Getting data from a TH03pro sensor into my platform from tuya cloud

Last week i got a WIFI temperature and humidity sensor: TH03Pro

And like always with these sensors: No direct access via WLAN possible. 
For this particular sensor it is possible to flash it with openBeken, but after all the things i read about the flashing, it is a little bit more complicated than flashing Tasmota on other devices (which i did several times).

The device is sending its data to tuya - so my idea is: get the data from tuya back to my raspberry pi, where all the data of my sensors is stored.

First attempt was:

Login to Tuya.ai and get an API key

 

By the way: login is done via QR code scanning from the smarthome app, which is used by the sensor 

But it turned out, that this was completely wrong. To get data out of the Tuya cloud you have to login to https://iot.tuya.com/

 

 So under "cloud" i had to create a project:

and create a API key:

After that i spent nearly 2h about authentication... With copilot forth and back... Always that error:

{"code":1004,"msg":"sign invalid","success":false,"t":1781356460593,"tid":"ca05aba1672911f1bf59122815ffe3c8"} 

The point is: With no device attached, you are not allowed to get a token. So how to add my device there? The default way is: Install tuya spatial on your phone 

  

This app starts with reading a QR code from the project of iot.tuya.com:

But then you have to login with an account - neither iot.tuya.com nor smart life worked...

So that is where this story ends for now - i am really disappointed. Getting data from such a cloud back was nowhere such a complex story. 

May be there is another approach, but up to now i really do not know, how to continue...