The https://auth.roblox.com/v2/login endpoint is not accepting valid funcaptcha tokens. See below for a reproduction.
As we can see the user in this reproduction has received a FC token for successfully completing the captcha. Afterwards a post request is sent to the login endpoint with the token and we can see the result below.
A few of my friends and I have been working on a bot to manage a group of ours and we noticed this issue when attempting to login to the bot account via a server we rent. After we noticed this issue I personally attempted to login using my own IP which is residential and surprisingly this issue was not present. One of the developers then attempted to login using his IP address and even though he had the same ISP as me, his login requests were blocked and the reproduction seen above was done with his IP address. The other developer on the project also confirmed this was an issue on his end as well.
It appears that you guys are doing some risk assessment of IP addresses that are being used on the login endpoint, this is an industry standard but if the endpoint is already protected by a captcha what is the point? As of now legitimate users are being affected as they are unable to login and as the response from the API is misleading, people are unsure as how to resolve the problem.
We appreciate that Roblox is looking to protect its users but would also appreciate having the login functionality restored to the many users that are currently affected.