I am having the same issue yaml: line 1: mapping values are not allowed in this context. Pipelines are locally converted successfully with drone jsonnet --stream.
Running single jsonnet pipelines are running fine on server side.
I have configured drone with native jsonnet support and I am running drone 1.9.0.
@netumoliver you can find the source code and unit tests at the below link. There is code and unit tests to handle single-pipeline and multi-pipeline configurations and they are passing. So your best bet is to probably triage the code
You should also make sure your file has a .jsonnet suffix otherwise it will not be converted from jsonnet to yaml.