Print-on-demand rejects more artwork than it accepts, and it is almost never because the design is bad. It is because the file is wrong.
So I asked Quodara for a t-shirt graphic with the production requirements stated up front: transparent background, limited colour count, bold shapes, no thin outlines, nothing that relies on a white background to make sense. What came back went through the printer's preflight without a single flag.
The design itself is clean — a heavy retro sunburst with a stacked slab-serif wordmark, four colours, high contrast, and it reads from across a room. The letterforms are correct and the counters in the letters are open enough that they will not fill in on a dark garment.
That last detail is what separates something you can actually sell from something that looks fine on screen and prints as a blob.
Six designs, one chat, one sitting. My previous route was a marketplace freelancer and a three-day turnaround per design.
If you sell merch and your bottleneck is artwork rather than ideas, the prompt below is written for the printer, not for the screen.