custom action and manual button cannot work

Tom,
Glad to help, as always.

For the custom object title, you can't use PHP code in that box. It's just a simple way to set static tags across all the pages that that object affects. To do something dynamically, you'd need to create an opengraph plugin. They're meant to be very easy to create, and if you copy the Open Graph - Custom plugin to your own, you could use the same features as custom and change a few lines to automatically set the og:title tag as well.

On a side note, what component are you working with? We always like to know what users are creating custom objects for because, if we get enough requests, we'll look into making a dedicated Open Graph plugin for it.

Best of luck,
Alex