Error when creating AWS Budget Actions to automatically stop EC2 and RDS

I use one EC2 instance and one RDS to run my Backend for my website. Now I saw that you can create an AWS Budget Action to automatically stop your EC2 or RDS instance. That wasn't possible before and I definitly wanna use it to be 100% sure not to get a fat bill from AWS. I already set up a billing alert, but I want the EC2 and RDS to also be automatically shut down, just to be really safe.

So when creating a new budget in AWS Budgets you can add a "Budget action", which requires you to attach an IAM role to AWS Budgets. I tried that with an existing EC2Role of mine, which has "AmazonEC2FullAccess" Policy attached to it. But this doesn't seem to be the right policy:

Ok I just figured it out after posting the question, the Role also needed a Trust relationship to AWS Budgets, which had to be attached to the Role in IAM: