Notes
Upload failed and nothing said why: what to check, in order
The file sat there, the bar filled, and then nothing — or a red line that only said "something went wrong". Here is the order to check things in, cheapest first.
First, rule out the thing everyone blames
It is almost certainly not the resolution. None of the four platforms publishes a DPI below which an upload is refused. Printful frames low resolution as a quality warning to check before you submit. Printify will even upscale a low-resolution file on its own before sending it to production. Amazon's editor refuses to enlarge your artwork, but it accepts it. Redbubble simply lists a minimum pixel count per product and says nothing about density at all. Low resolution ruins the printed product. It does not usually stop the upload. If the upload itself failed, something more mechanical is wrong — and the five below account for nearly all of it.
The five checks, in order
- Is it a WebP?This is the most common silent failure and the easiest to miss. Not one of the four platforms accepts WebP — Printful takes PNG and JPEG, Printify adds SVG, Redbubble is JPEG and PNG only, Merch is PNG alone. Several design tools and most "save image as" flows in a browser now hand you WebP by default, so a file can look perfectly normal and be the wrong type. Re-export as PNG; it is the only format all four accept and the only one of those that keeps a transparent background.
- Does the file name have two dots?Printful states this outright: a name like `design..png`, with two dots before the extension, results in a failed upload. Export scripts and batch renamers produce that shape more often than you would expect — strip the duplicate and it goes through. Nothing in the error message will tell you this.
- How big is the file, really?Check the actual megabytes, not the dimensions. Merch by Amazon stops at 25 MB, and a transparent PNG carrying any gradient or grain crosses that easily. Printify allows 100 MB, or 20 MB for SVG. Printful allows 200 MB. Redbubble allows 300 MB. A file that uploaded fine to one platform can be refused by another on size alone.
- Are the pixel dimensions inside the window?There are ceilings as well as floors. Printful refuses anything over 20,000 px on a side; Redbubble refuses over 13,500. At the other end, Merch needs more than 485 × 485 — and note that the old requirement of exactly 4500 × 5400 was dropped, so a file failing because it is not that exact size is not what is happening any more.
- Is it RGB?Merch by Amazon requires artwork created in an RGB space and converts to CMYK itself for printing. Redbubble asks you to design in CMYK if you like but convert to RGB before uploading. A file still carrying a CMYK profile is a real cause of trouble at the door, and it is invisible in a thumbnail.
Batch, auto-fix and exports
Everything above is free for one file at a time, and always will be. Doing it to a whole folder — batch checking up to 100 files, one zip with every platform file for every design, and a CSV report — is part of Seller.
Exports are padded and centred to each platform's size on a transparent canvas. Nothing is ever upscaled — a file enlarged to pass a dimension check still prints soft, which is the failure this tool exists to prevent.
If all five pass and it still fails
Two things are left worth trying before you write to support. If the file is a PDF, flatten it — Printful accepts PDFs but warns that hidden layers, embedded fonts, blend modes and transparency effects can render unpredictably, and an upload that chokes on one of those gives no useful message either. And if the file has been through several round trips between tools, export a fresh copy from the source rather than re-saving the one that failed; a corrupted or truncated file looks identical in a file browser. When you do contact support, say which of the five you have already ruled out. It changes the reply you get.
Frequently asked questions
The error said "resolution too low". Is that not a resolution problem?
That specific message usually comes from a product-level minimum rather than a density check — Redbubble will not let you enable a product whose minimum pixel count your file does not meet, for example. It is a pixel-count problem, not a DPI-tag problem, and changing the DPI number in your file properties will not move it by a single pixel.
Why does the same file work on one platform and fail on another?
Because the four differ on every axis that matters: accepted formats, file-size ceiling, pixel ceiling and floor. Redbubble takes a 300 MB file that Merch refuses at 25 MB; Printify takes an SVG that Redbubble will not. A file is never simply valid — it is valid for a platform.
Can I just compress it until it works?
Compressing is the right move when the ceiling is the problem, but do it in the order that costs you least: trim the empty transparent margin first, since that is free and Amazon asks for it anyway, then reduce colour depth, and only resize the canvas as a last resort. Never enlarge afterwards to get back to a round number.