Registration captcha again

[netgab]

Hi team,
want to register a new land line, without SMS support. Guess Captchas are enforced by now, because upon registration, I'll get the notification ""Captcha required for verification, use --captcha CAPTCHA\nTo get the token, go to https://signalcaptchas.org/registration/generate.html\nAfter solving the captcha, right-click on the "Open Signal" link and copy the link.\n""

There are various docs/ discussions, which are

1. sometimes quite old (guess Signal changed stuff in the meantime)
2. are a little bit confusing (at least for me).

I want to get the proper facts now (perhaps for the Wiki with exact working instructions :)

The steps on my side are now:

Open [https://signalcaptchas.org/registration/generate] and solve the captcha. After this a link is displayed to open signal with a URL starting with signalcaptcha://

This is the first step with a lot of variants, how to proceed from here. There are rumours, to:

1. Create (somehow) a token using the data in the link destination (no clue how to do this)
2. Just copy the full link (example value: signalcaptcha://signal-hcaptcha.<VALUE1>.registration.<VALUE2> ) and use this
3. Remove signalcaptcha:// from the link above and use the remaining part

Note: Sometimes, the link begins with signal-hcaptcha (very long VALUE2) - sometimes it is signal-hcaptcha-short.<VALUE1>.registration.<VALUE2> (short VALUE2). I could not reproduce when the captcha generator generates what variant.

There are other posts, which states to put the captcha (or parts of it?!) in single quotes. But there are no examples for this.

At the end of the day, I'm always getting the response, that an invalid captcha is given. After some retries, I get rate-limited.

Does anybody have a working approach? At the moment it's a try and error approach on my side, which doesn't make any sense. There must be a single working way and not tons of non-working variants :)

I know this is probably not the problem of this project here - it's a Signal issue. But maybe someone knows how to tackle this.

[LFrank2021]

Hi @netgab

I had to re-register my system and wrote my successful steps here

Is this helpful?
Especially the IP-part was a brain-wrecker for me.

Best regards

[netgab]

Hi @LFrank2021 ,
wow - I thought it was just me with the deregistration. Thanks for the post. I'll try to follow these steps.
To be honest, I'm using the signal-cli REST-API wrapper from https://github.com/bbernhard/signal-cli-rest-api

The Dockerfile is using the latest signal-cli 0.14.2 version with SPQR support.
So it could be some incompatibality on this side as well. Gonna try it with signal-cli natively to see if this succeeds..

Thanks again...

Edit: The sources in https://github.com/bbernhard/signal-cli-rest-api use the latest signal-cli version 0.14.2, but the
latest stable release at Dockerhub is using the version 0.14.1 (which is still somehow affected, based on the original thread).
This explains stuff.

Nevertheless, If I got this working, I'll check the docs around and try to get rid of outdated captcha howtos...

[LFrank2021]

I think this might be helpful with your docker setup.
I have no experience with signal-cli & docker so I am of not much help here.

[LFrank2021]

And I found this again
https://github.com/AsamK/signal-cli/pkgs/container/signal-cli/777029315?tag=latest

This should be the 0.14.2 docker image. 🤞

[netgab]

So I used the latest image now and used signal-cli within my docker container.
I guess the confusing part after the captcha verification is, that an exception is raised Failed to register: StatusCode: 400 (InvalidTransportModeException):

signal-cli -v --config /home/.local/share/signal-cli -u +4312345 register

# Hint to do a captcha verification. After the captcha is solved and the token is generated (copy link)
signal-cli -v --config /home/.local/share/signal-cli -u +4312345 register --captcha signalcaptcha://<LONG-TEXT>

Now signal-cli raises an exception like:

2026-04-19T05:48:07.124Z [main] DEBUG org.asamk.signal.util.IOUtils - XDG_RUNTIME_DIR not set, falling back to temp dir
2026-04-19T05:48:07.129Z [main] DEBUG org.asamk.signal.App - Starting signal-cli 0.14.2
2026-04-19T05:48:07.840Z [main] INFO  com.zaxxer.hikari.HikariDataSource - HikariPool-1 - Starting...
2026-04-19T05:48:07.912Z [main] INFO  com.zaxxer.hikari.pool.HikariPool - HikariPool-1 - Added connection org.sqlite.jdbc4.JDBC4Connection@76318a7d
2026-04-19T05:48:07.913Z [main] INFO  com.zaxxer.hikari.HikariDataSource - HikariPool-1 - Start completed.
2026-04-19T05:48:09.412Z [main] INFO  com.zaxxer.hikari.HikariDataSource - HikariPool-1 - Shutdown initiated...
2026-04-19T05:48:09.413Z [main] INFO  com.zaxxer.hikari.HikariDataSource - HikariPool-1 - Shutdown completed.
Failed to register: StatusCode: 400 (InvalidTransportModeException)
org.whispersystems.signalservice.api.push.exceptions.InvalidTransportModeException: StatusCode: 400
        at org.whispersystems.signalservice.internal.push.PushServiceSocket$RequestVerificationCodeResponseHandler.handle(PushServiceSocket.java:2288)
        at org.whispersystems.signalservice.internal.push.PushServiceSocket.makeServiceRequest(PushServiceSocket.java:1429)
        at org.whispersystems.signalservice.internal.push.PushServiceSocket.requestVerificationCode(PushServiceSocket.java:315)
        at org.whispersystems.signalservice.api.registration.RegistrationApi.requestSmsVerificationCode$lambda$3(RegistrationApi.kt:74)
        at org.whispersystems.signalservice.api.NetworkResult$Companion.fromFetch(NetworkResult.kt:56)
        at org.whispersystems.signalservice.api.registration.RegistrationApi.requestSmsVerificationCode(RegistrationApi.kt:73)
        at org.asamk.signal.manager.util.NumberVerificationUtils.requestVerificationCode(NumberVerificationUtils.java:96)
        at org.asamk.signal.manager.internal.RegistrationManagerImpl.register(RegistrationManagerImpl.java:141)
        at org.asamk.signal.commands.RegisterCommand.register(RegisterCommand.java:81)
        at org.asamk.signal.commands.RegisterCommand.handleCommand(RegisterCommand.java:52)
        at org.asamk.signal.commands.CommandHandler.handleRegistrationCommand(CommandHandler.java:33)
        at org.asamk.signal.App.handleRegistrationCommand(App.java:268)
        at org.asamk.signal.App.handleCommand(App.java:177)
        at org.asamk.signal.App.init(App.java:147)
        at org.asamk.signal.Main.main(Main.java:56)

Dispite of this error, the captcha verification was successful and the voice request can be issued.