I just merged a patch that adds a run.sh script at the root of the project [1]. You should use it to run foxbox.
The reason is that I merged the dnschallenge component into foxbox, and so foxbox now has 2 binaries. As a result we need to use cargo run --bin foxbox to run foxbox as cargo has no concept of default binary.
As a nice little sugar the script also adds target/debug to your PATH so that the dnschallenge binary is in the PATH; as a result the letsencrypt challenge shoud just work.
Note this script is very simple and only done for development environments; for example it won’t work properly when you use --release (but won’t warn you 
).
[1] https://github.com/fxbox/foxbox/commit/ecc92fae61141185046ceaa7131a53a44258d4b4
–
Julien