If customer made an online purchase of $100 but gets charged $150, is the dispute amount $50? It's not the $150 since customer did authorize $100, correct? Is this even a REG E dispute, since customer authorized it?

Thank You.

1005.11 defines an EFT error as an "incorrect electronic funds transfer."

There are many more error types than simply unauthorized. Yes, the error is $50 and it is covered by Reg E.