Rewrites to an external API return 508 Loop Detected

I have this rewrite in driftline.json:

{ "rewrites": [{ "source": "/api/:path*", "destination": "https://api.example-shop.dev/:path*" }] }

Any request to /api/products now returns 508 Loop Detected. The external API is also hosted on Driftline, in a different team.

Is the external API project also rewriting /api/* somewhere? Two projects rewriting into each other is the classic way to get a 508.

Checking — the API project has a catch-all rewrite to its own /api/index. Could that count?