Change cpython version

Is there any way to change the python version used by the buildpacks? I saw on the paketo buildpack documentation a possible way, but it does seem to work in my fly.toml file. It is posted below:

[build]
builder = “paketobuildpacks/builder:base”
[[build.env]]
name = “BP_CPYTHON_VERSION”
value = “3.9.14”