If you chose “Text me a sign-in code” on the sign-in page, you were sent a code, the code was accepted, and you were then told we could not finish signing you in. There was no way through it and nothing you could have done differently. We are sorry — that is a bad thing to meet at the front door.
The cause was on our side and it was not specific to your account. Sending and checking the code worked correctly the whole time; what was missing is the step that connects a phone number to a SIMCOAI account. No account has a phone number recorded against it yet, and there is no way to add one, so that sign-in method could not have worked for anybody.
The option has been removed from the sign-in page rather than left there to fail. Signing in with your email address, with a code sent to your email, and with Google all work exactly as before and were never affected. If you are stuck, use your email address.
A correction, and an apology. Our first fix removed the option, which stopped anyone new from hitting it — but it did nothing for people who had already signed in that way. If you had, your browser was still holding a sign-in session for your phone number, and pressing “Try signing in again” quietly reused it instead of showing you the sign-in form, so it failed again straight away, every time. Signing out did not clear it either, because the sign-out link pointed at a page we retired earlier this month that sent you back into signing in. Both are fixed: retrying now always shows you the sign-in form, and signing out genuinely signs you out. If you are still on the error page, reload it once and press “Try signing in again”.
We will bring sign-in by text back once you can add and confirm a phone number on your account from the Security page, so the code arrives somewhere we can actually match to you. No account was changed, no sign-in details were exposed, and nothing was recorded against your account by the failed attempts.