You need to run Shopify CLI with --tunnel-url
flag, for example:
shopify app dev --tunnel-url=https://extensions-domain.ngrok.dev:3001
If you need ngrok for app as well, create ngrok.yml
file in the root of the project and enter:
version: 2
authtoken: paste_ngrok_auth_key_here
tunnels:
first:
proto: http
addr: 3000
domain: app-domain.ngrok.dev
second:
proto: http
addr: 3001
domain: extensions-domain.ngrok.dev
And run it with
ngrok start --config ngrok.yml --all
This might be limited to paid Ngrok plan, although I highly recommend it as it never failed me over the years.