Q: locked out of my iphone 6plus

I think it is prompting you to enter a 4-digit code to use in addition to fingerprint.

Hi there!

When you set up the Touch ID, is specified that you need to enter the 4-digit code each time you restart the device.

If you don't know it, you need to reset your device:

Use iTunes to restore your iOS device to factory settings - Apple Support

If you can't back up or restore your iPhone, iPad, or iPod using iTunes - Apple Support

Thank you for using Apple Support Communities.

All the very best,

James