Wrong identifier
Check country codes or email spelling without guessing or using another person's details.
First check whether the system requests a username, phone number or email. A display name is not always a login identifier. Extra spaces and an unintended keyboard language can cause mistakes.
If the password is rejected, inspect autofill. Saved credentials may be outdated after a password change. When the identifier is correct but access still fails, follow the applicable recovery instructions.
Look for actual confirmation of a successful sign-in. Pressing a button or opening another page is insufficient. This explanatory page does not sign you into an account.
These points separate the practical questions raised by this subject. Read each one in the context of the conditions described above.
Check country codes or email spelling without guessing or using another person's details.
Confirm your current credentials before replacing stored information.
Pause if a code, permission request or new-device message does not match an action you initiated.

Inspect the identifier with autofill disabled. Separate credential errors from page-loading errors. Connection and browser checks are relevant to loading failures.
Sign out after using a shared device and avoid saving credentials. Closing a tab does not necessarily end a session. Check that the next person cannot see your information.
Do not enter details after an unexpected redirect.
Correct extra spaces or unsuitable autofill.
Where available, use instructions delivered to your own contact details.
Sign out and remove personal information on shared devices.
Use the applicable recovery process. Do not ask someone to recover access by giving them your password.
Do not share it. Review account security and whether you reused the password elsewhere.
Loading a page and verifying an identity are separate. Use the exact error to distinguish credential and session problems.
Send the time, device, browser and error message with private information removed.