On admin/config/drupalchat/configuration you can set the DrupalChat Visibility.
If you set it to PHP (Option 3 "Pages on which this PHP code returns TRUE (experts only)") the entered PHP code does not seem to be executed properly in Version 2.8. It did in 2.5. As an example I tried a simple return false.
I looked into the drupalchat.module and on line 67 there's a check_plain()-function introduced. Probably for security reasons. But maybe this does not make sense for a PHP Code field? I removed it and it worked again. Maybe you can fix this for the next release. (i'm no developer)
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2.0
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