Set the scale to 100%, never "fit to page"
"Fit to page" tells the printer to shrink whatever it is given until it fits the media. Hand it a 210 × 297 mm A4 page and a 101.6 × 152.4 mm label, and it will faithfully shrink the entire sheet, margins included, onto your sticker. The shipping label ends up roughly a third of its intended size.
Set scale to 100% (some drivers call it Actual Size or None) and give the printer a page that is already the size of the label. A cropped 4×6 PDF printed at 100% comes out edge to edge.
This is also why the label sometimes prints correctly for one seller and badly for another on the same printer model. It is a document and driver setting, not a hardware difference.
Match the page size to the media
The printer's page size, the label stock in the printer, and the PDF's page size should all be the same number. If any two disagree, something gets scaled or clipped.
For a 4×6 roll, all three should be 101.6 × 152.4 mm. Set the media size in the printer driver, not only in the print dialog, because the driver default overrides the dialog on several common Windows setups.
203 DPI or 300 DPI?
203 DPI is enough for a standard 4×6 shipping label. The bars on a courier barcode are wide enough that both resolutions produce a scannable code, and 203 DPI is what most Indian sellers already own.
Step up to 300 DPI when you need small text to stay legible, when you print dense codes such as Data Matrix on small stickers, or when your barcode has to be printed at under about 25 mm wide. For Flipkart, Meesho and Amazon shipping labels at full size, the higher resolution does not change whether the courier's scanner reads the code.
If a barcode is not scanning on a 203 DPI printer, resolution is rarely the reason. Work through the next section before buying hardware.
Why a barcode fails the courier scan
Scaling is the usual culprit. A barcode printed at 85% is not a smaller valid barcode. Shrinking narrows the bars and the quiet zone until the scanner cannot resolve them. This is the most common cause and it traces straight back to "fit to page".
Clipping is next. Barcodes need clear space either side, called the quiet zone. A crop that cuts close to the bars removes it, and many scanners then refuse the code even though every bar is present.
Darkness may be set too low or too high. Too low leaves pale bars with soft edges. Too high lets the heat bleed sideways, thickening the bars until the ratio between bar and space is wrong. Print a test label, and adjust in small steps until edges look crisp rather than grey or blotchy.
A dirty printhead shows up as a thin white line running down the label, usually adhesive or dust. Clean it with isopropyl alcohol on a lint-free cloth with the printer switched off. A white line crossing bars will fail a scan every time.
Occasionally the stock is simply loaded upside down. Direct thermal paper only darkens on its coated face. Loaded the wrong way round, you get a faint or blank label. Scratch the surface with a fingernail: the coated side marks grey.
When the printer skips labels or prints across the gap
Run the printer's media calibration (often called gap or auto-sense calibration). It teaches the gap sensor where one label ends and the next begins. Any time you switch roll size, brand of stock, or move from gap labels to continuous, calibrate again.
Zebra, TSC and Xprinter units all expose this differently. It is usually a button hold at power-on, or a utility in the vendor's setup tool.
A working recipe
- Crop the marketplace A4 down to just the shipping label.
- Load 4×6 stock and run media calibration once.
- Set the driver media size to 101.6 × 152.4 mm.
- Print at 100% scale, not Fit to Page.
- Print one label, scan it with a phone barcode app before printing the batch.
That last step costs one sticker and catches nearly every problem before it becomes a pickup failure.