You vacuumed. You went over the seat twice, you got the crumbs out of the seam with the crevice tool, and when you stood back the fabric still had that dull grey cast across the middle of the cushion. It is not dirt sitting on top any more. It went in.

Car upholstery is woven, and a weave has a top surface and an inside. Every time someone sits down, whatever is on the surface gets pressed through the gaps and into the fibre. Suction pulls at the opening of that gap; it does not reach around the fibre. That is why the seat can be genuinely clean of loose debris and still look tired.

What matters here is that the stain has to be brought back out the way it went in. The cleaner wets the fibre, breaks the bond between the soil and the material, and floats it up to where a towel can take it away. The towel is doing the removal. The bottle is only making the removal possible.

That changes the procedure in one specific way. Spray, agitate with a brush, then blot with a dry towel and keep turning the towel to a clean face. If you spray and wipe with the same side, you are moving the loosened soil across the panel and pressing some of it back down, which is exactly the grey cast you started with.

The honest limit. This is a fabric and plastic cleaner. On leather it will strip the finish oils and leave the hide dry, and there is no fixing that afterwards with the same bottle. If the seat is leather or coated vinyl, this is the wrong product and the right one costs about the same. Read the seat before you read the label.