Hi Jose,
thank you for your fast answer. I was already spending quite some time on debugging.
For me it is not clear then, why a firmware for RPI 3B+ in Combination with RAK 2245 is provided by RAK if it cant be used.
Anyway it would be benefitial for the Helium Network if it was possible to join using 3rd party hardware. I have a RAK831 a RAK 2245 and a RAK 7249 left, that i would like to connect.
If the Firmware for the RAK Hotspot Miner was available i could port it to the other Hardware.
So i have four questions ?
Is every RAK Helium Miner provisioned with a unique certificate issued by Helium?
Is it possible to request a certificate for 3rd party gateways?
Is there a service running on the RAK Miner, that is responsible for establishing a bluetooth conneciton for 5 Minutes to connect to the app?
Is this service available for me 
Best regards and thanks for the help
Simon