The issue you describe is consistent with what is described in this thread:
A few hardware releases cannot be upgraded to the latest firmware and end up in a locked state. If it is the case for you Gotenna will exchange the unit.
Yes, I think mbmesh has suggested the issue correctly. In post 209 in the Mesh 5.0 is here! thread he cited, there’s more info to help. You can contact them directly for further help at: support@gotenna.com
I received a mail from goTenna support advising me to try with an iOs device and the goTenna app.
I tried this operation last night and it worked perfectly : the updating processus continued and the goTenna upgraded finally with the right FW version !!!
After upgrade, I tried it with an Andrdoid smartphone, and all was OK.