Hi @Morsella
There are currently problems with OneNumber to connect your Apple Watch. Follow this topic and you will stay informed. Very annoying, but that's the way it is.
This is now the update from Vodafone. Follow the topic I just provided and you will stay informed:
Just a little update from this side. It is currently not possible for customers to order OneNumber. Customers experience a "connection failed" message or cannot select the "Configure mobile network" button. As soon as we have an indication of when this will be possible again, I will share it here. Current customers with OneNumber can continue to use the service, but cannot transfer OneNumber to another Watch at this time."