Another Homebrew Item Question (Temp HP)

Trying to create a Home-brew item which will increase AC and add some Temp HP. I can get the AC to display when the item is activated, but I can't get Temporary HP to budge at all. Is Bonus the wrong modifier for this? What should I do instead?

Are you trying a fixed number, a modifier, or a die roll?

Is it supposed to be permanent or temporary? Temporary effects are not supported at this time.

Fixed number, and I guess temporary. If that's just not a thing yet, I'll find something else.

Again, thank you.