If your PhantomBuster Phantoms fail with 'Missing cookie' when launched from n8n, the cookie probably never left n8n: their PhantomBuster node sends unfilled optional fields as empty {} arguments, so the session cookie you configured gets dropped. PhantomBuster's own support team filed this bug and their workaround is to use n8n's generic HTTP Request node instead of the native PhantomBuster node. It is a node-level serialization bug, not your credentials.

Context: n8n issue 18087, filed by Anna from PhantomBuster's own Customer Care team: when optional fields in n8n's PhantomBuster node are not filled in, n8n sends them to Phantoms as empty {} arguments. On PhantomBuster's end this surfaces as 'Missing cookie' - the mandatory session cookie never makes it from n8n to the Phantom. Their documented workaround: use n8n's generic HTTP Request node instead of the native PhantomBuster node to make things work smoothly.