Digitalia The "I am a human" CAPTCHA test fails repeatedly
Developer-Dude Maybe you're IP address?
If that is the case, starting being a human should help with your issue.
Jokes aside, as mentioned, it seems that your problem is VPN related.
If you receive "too many attempts" error after just one there is a good chance other people used the same exit node.
If your VPN allows you, change exit node.
I use Signal (through Molly) with VPN without any issue.
I am asked to pass the human test only when I start too much new conversation in a short timeframe.
Also, did you notice if the SMS code arrives with great delay?
Also, I am not sure about Signal, but just today with a friend, we encountered the very unsettling behaviour on Whatsapp, telling the system is not ok only with a specific phone number, with other three phone numbers it went ok.
To rephrase it, every attempt with phone_number_1 always led us to an error from Whatsapp complaining about the OS, while phone_number_2, phone_number_3 and phone_number_4 worked as intended, no matter what the order and how many exploit compatibility options we used.