iosmall is your client ID really 64 chars long ? That doesn't sound right. All the GitHub Client ID I've seen are 20 chars long. Did you switch Client and Secret, maybe pasted the secret after the client ID in the same field ?
But it doesn't sound like that either because my client secrets are 40 chars long, so neither, 20, 40 or 20+40 give 64 chars...
Make sure you copied the right credentials from the GitHub dashboard.
In any case if the secret has indeed been pasted in the client ID field, you should revoke it as it's now been publicly exposed.
One thing I notice now: what tutorial are you referring to ?