Keyframing in transitions

I can't seem to be able to move a keyframe into a transition. It's a resize effect that should obviously start right when the first bit of the clip is visible. But when I try dragging the keyframe into the transition, it would always snap back.

Try setting a new keyframe at the correct frame and then deleting the current one.

Try setting a new keyframe at the correct frame and then deleting the current one.

I will give that a try, thank you!