OAuth callback with php, what am I doing wrong?

Your response_type is force_verify

it should be code for this example

Line 27 of this example shows a URL being constructed.

ClientID’s are public there is no need to hide this

Should be

https://id.twitch.tv/oauth2/authorize?client_id=<myid>&redirect_uri=http://plox.nu/oauth/callback.php&response_type=code&scope=bits:read

You can optionally add

https://id.twitch.tv/oauth2/authorize?client_id=<myid>&redirect_uri=http://plox.nu/oauth/callback.php&response_type=code&scope=bits:read&force_verify=true

if you need Force Verify