Oh I totally forgot to mention the existing Let’s Encrypt cert. If the Let’s Encrypt certificate json file is still in the data directory it seems to use that first and ignores your config. So you should delete that json file. It should be at:
.anvil-data/letsencrypt-certs.json
The anvil data folder is located one level up from the app code by default. I think I launched and closed the app at least 100 times trying to get everything right.