Trying to add HP as a modifier but doesn't work tried as set tried as bonus. Is there a workaround other than manually adding?

The HP modifier doesn’t work, you’re just gonna hafta add the HP manually.

Got that but since this is a bug report maybe the fine folks at dndbeyond can look into fixing the problem. 

Allow me to rephrase. That modifier doesn’t do what you think it does, it’s for healing potions. So as far as DDB is concerned there’s nothing to “fix” until they make it so you can click a healing potion on your sheet and it will automatically heal you that much HP. Short answer, they ain’t gonna fix it.