Spinning up Instance with Chef 12 on OpsWorks stack

403 should be a permissions issue. I'm guessing the role or policy you set up is wrong somehow.

I realize this probably isn't helpful but I would avoid starting any new projects or migrating any existing projects to OpsWorks Stacks. As far as I can tell this is a dead product and has been for years. We have been promised a v2 version for a few years and each year staff comes on here saying it is on the roadmap for the current year. It isn't. I'd be happy to be proven wrong.

If you begin using Stacks now there are two possibilities. Either AWS suddenly produces v2 and now you are in a legacy product with no support that doesn't use Chef 12 or they never provide any updates at all because it already is unsupported and you'll have to migrate away at some point anyway.

The fact that next April is when every single AMI supported by OpsWorks Stacks will be EOL should mean one of these will happen in the next year.