Could not send: libsignal-service sending error

[hbbio]

When trying to send a first message, I get the following error:

Could not send: libsignal-service sending error: 
Proof of type ["captcha", "pushChallenge"] required using token xxx-xxx-xxx

The message still shows locally but wasn't sent. The status (error) is not shown again when relaunching giving the impression the message has been sent.