My I phone 6 wont let me log in with my apple id. It is saying incorrect info. What can I do?

Does the same Apple ID/password let you sign in other places?

Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.      

Did you acquire the phone second hand?