Hi @wrightak
If I understand you correctly, this vector filter should work. Unset your $SUBJECT and modify 18-23 with something like:
[transforms.remap]
type = "remap"
inputs = ["nats"]
source = '''
. = parse_json!(.message)
'''
[transforms.log_json]
type = "filter"
inputs = ["remap"]
condition = '.fly.app.name == "production-app-name" || .fly.app.name == "staging-app-name"'