@Tom Hoad Did you try without the apostraphes? like

- !ImportValue ${self:custom.sstApp}-TableArn

Yeh this results in invalid YAML

@Tom Hoad What type of Resource is it? This is typically how I do it:

aha! the Join did actually work, it was just my indentation that was wrong

Glad to hear it! 🙂 Good luck with your project @Tom Hoad