Amazon Echo as prefered thread Network

Hello, I would like to use my Echo Dot 4th generation as my preferred thread network. The Echo Dot appears as normal on other networks, but I cannot successfully send the credentials to Home Assistant via iPhone or Android phone. The iPhone tells me this as an error: No preferred network found and the Android phone tells me there are no credentials available to send. How do I make the Amazon Echo Dot my preferred Thread Network so I can use it to build my Thread Network?
Thanks in advance !