Services Shortcut in Mail?

Not strictly an Omnifocus question but in trying to set up Clip-o-Tron I noticed my keyboard shortcut for Send to Omnifocus isn’t working in Mail even though it’s configured in Preferences.

No shortcut available:

But I’ve configured the shortcut in the OS preferences. I tried adding another screenshot but apparently new users are limited to one image per post.

Anyone know what might be up?