POST to /v1/labels with 'label_format': 'zpl', 'label_layout': '4x6', and 'label_download_type': 'inline' alongside the shipment object
The API response will contain a label_download object with a 'href' URL and also a 'zpl' field when inline is requested; decode the Base64 ZPL string and spool directly to a Zebra printer
Alternatively set 'label_download_type': 'url' to receive a time-limited download URL valid for 90 days if you prefer deferred rendering
Confirm the shipment's carrier supports ZPL — not all carrier/service combinations return ZPL; fall back to PDF if the response label_format differs from the request
Do not request branded labels with ZPL format; branded label rendering is not supported for ZPL and the API will return an error
Known gotchas
ShipEngine is being rebranded as ShipStation API; all existing /v1/ endpoints remain unchanged and no migration is required
ZPL label URLs expire after 90 days; cache the raw ZPL string if you need to reprint after that window
Label rotation is supported for ZPL and PDF but not PNG; pass the 'label_image_id' rotation parameter only when using one of those two formats
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