fly.io ENV available in Dockerfile

Question

Im trying to access env variables that are specified in the fly.toml file in the Dockerfile when running flyctrl deploy however they are always showing as empty strings. Am i doing something wrong here?

[env]
  API = "ABC"

ARG API
ENV API $API
RUN echo $API // prints Run echo

Answer 1

Turns out this can be done with '[build.args]'

[build.args]
  API = "ABCD"