Recommended flow
Capture the exact ZPL payload, preview it, store a PNG/PDF proof with the ticket, then print a final hardware sample only after the cheap checks pass.
Minimal request shape
The browser preview uses a simple ZPL plus density request. Keep generated label data redacted in logs and tickets.
POST /api/preview
Content-Type: application/json
{
"zpl": "^XA...^XZ",
"density": "8"
}