Pigeon does not send notification

[timrab]

when notification is triggered, following error is shown in the pigeon/merlin log:

022-05-20T17:08:40.918+00:00,2,runprog.go:255,[2] Executing job 24 : '/usr/bin/php' with ["common/pigeon/pigeon.phar" "event:post" "workflow_ended" "{\"workflow_id\":6,\"job_id\":24,\"status\":2,\"started_at\":1653066519,\"ended_at\":1653066520}"] 2022-05-20T17:08:41.042+00:00,4,runprog.go:304,[2] Program '/usr/bin/php' failed (-1): 'exit status 255'
maybe it requires proximity or other dependencies?