Implicit grant

[noontimedeveloper]

Looking at the code it seems to be using authorization code flow , when i turn off the implicit grant on app registration , i get the following error
"OpenIdConnectMessage.Error was not null, indicating an error. Error: 'unauthorized_client'. Error_Description (may be empty): 'AADB2C90057: The provided application is not configured to allow the 'OAuth' Implicit flow.

Can you please help explain why do we need to turn on implicit grant on this ?