Why the buds died? Is this a failed grafting?

Hi.

I watched some grafting videos and decided to try it on my own.
I tried this on a bougainvilla plant. What I did was splitting the plant stem by half, and put another variety in the middle. I then wrapped them with a tape and enclosed them with a transparent plastic, then wrap the end of the plactic shut.

When I noticed 2 buds starting to appear, I poked a hole on each. I also didnt tie the plastic back so air could get in. They looked great.

Until at some point both buds died one after another.

Is this a failed grafting? What is my mistake and what can I improve?
I haven't open the tape yet because I still have hope that they will work. No water got in.

Thanks!