Quick checklist
- Label size set to 100×150 mm (4×6″) and Scale = 100% in the print dialog.
- Thermal printer driver + firmware updated; media set to Label, 203–300 DPI, correct orientation.
- Browser pop‑ups allowed for your domain; try another browser if needed.
- Plugin/portal set to PDF if your printer doesn’t support ZPL/EPL natively.
- Carrier service successfully generated a label (no API/credential errors).
7 fixes that solve most label problems
1) Force the correct label size & scaling
- In the print dialog, set Scale: 100% and paper size to 100×150 mm (or 4×6″).
- Disable Fit to page/Shrink to fit. Turn off headers/footers.
- In your printer preferences, choose the matching paper size and DPI.
2) Switch output format (PDF vs ZPL/EPL)
- If you get blanks/garbage characters, your printer likely isn’t speaking ZPL/EPL. Switch the carrier/plugin output to PDF.
- If you must use ZPL/EPL, install the vendor driver and send labels via a compatible spooler.
3) Update or reinstall printer drivers
- Install the manufacturer driver (Windows/Mac) rather than a generic class driver.
- Remove old drivers/queues; re‑add printer with media size = 4×6″.
- Update firmware if labels are intermittently blank or rotated.
4) Allow pop‑ups & fix blocked downloads
- Allow pop‑ups and redirects for your WooCommerce admin and carrier portal domain.
- Disable extensions that intercept PDFs (ad blockers, privacy filters) and retry.
- Clear the browser cache for the site; try a private window or another browser.
5) Use the system print dialog (or download first)
- If in‑browser print previews mis‑scale, click Download and print from a desktop PDF viewer (Adobe/Preview).
- From the system dialog, re‑confirm 100×150 mm and 100% scale.
6) Check carrier/plugin service mapping
- If the label fails to generate, the selected service may be invalid for weight/dimensions/destination.
- Re‑map WooCommerce shipping methods to real carrier services; verify credentials and contract permissions.
7) Fix rotation & darkness (print quality)
- Set orientation to Portrait. If still rotated, set Auto‑rotate off and rotate 90° manually.
- Increase darkness/heat in printer preferences; set media type to Label.
- Calibrate the printer (feed/align) after changing label stock.
Symptoms by carrier
Royal Mail (Click & Drop)
- No label after "Generate": check order imported & postage applied; ensure label format = 6×4″.
- Blank PDF: retry via Reprint; if persistent, switch browser.
Evri Business
- Wrong size: portal often defaults to A4; change to 4×6″ per printer.
- CSV imports: ensure dimensions/weight tiers valid or the service is rejected silently.
DPD / DPD Local
- Label won’t generate: check consignment settings and service permissions (Next Day/Saturday).
- Multi‑parcel: enable one‑label‑per‑parcel; verify parcel count matches contents.
General plugin notes
- After updates, re‑save plugin settings to refresh API tokens and webhooks.
- Conflicts: temporarily disable unrelated PDF/printing plugins and retest.
Advanced checks
- HTTPS & mixed content: print widgets hosted over HTTP may be blocked by browsers; use HTTPS everywhere.
- Local print bridges: If using a local bridge (e.g., Java/desktop print helpers), ensure it’s running and allowed by OS firewall.
- Workstations: Lock label size via OS printer defaults so every user prints consistently.
Pro tip: Test with a known‑good sample label (100×150 mm PDF). If that prints correctly, the issue is with service mapping or the plugin, not the printer.
Skip the headaches: auto‑print on scan
ParcelOffice: rules → labels → tracking
Instead of opening print dialogs, ParcelOffice chooses the right carrier per order and prints labels automatically when you scan the order at the bench. Tracking writes back to WooCommerce.