X (Twitter) "Add an existing account" not working on Chrome

Having trouble adding your other Twitter account to the app? You’re not alone. Many users have encountered the dreaded “Add Existing Account” issue.

Make sure you have a stable internet connection.
Double-check your login credentials. A typo in your username or password can easily trip up the system.

Possible Fixes (Chrome)

Cache and Cookie: Head to your Chrome settings. Under “Privacy and security,” find “Clear browsing data.” Select “the beginning of time” for the time range and tick the boxes for “Cookies and other site data” and “Cached images and files.” Then, with a mighty click, hit “Clear data.”
Incognito: Ditch incognito mode. Open a regular Chrome window and try logging in with your username and password.
Extension: One by one, disable your Chrome extensions and see if the issue resolves. If it does, you’ve identified the extension causing the conflict. You can then keep it disabled or find a suitable alternative.

Sometimes, a simple app restart can work wonders. Close the Twitter app completely (swipe it upwards on iPhones or force close it on Android) and relaunch it. Try adding your account again.
Log out of your current Twitter account and then attempt to log in using the “Add Existing Account” feature. This can refresh the login process and potentially resolve the issue.
Outdated apps can sometimes develop glitches. Head over to your app store and see if there’s a waiting update for Twitter. Updating the app can often patch known bugs, including login issues.
If the above solutions fail, a complete app reinstall might be the answer. Uninstall the Twitter app and then download it again from the app store. This will ensure you have the latest version and a clean slate for login attempts.
Sometimes, the problem might lie with Twitter’s servers. If none of the above solutions work, consider reaching out to Twitter Support. You can find their support page through the Twitter website or app. Briefly explain the issue and provide any relevant details to help them diagnose the problem.