Wilson's Moss Killer. Problem need help

I have contacted the manufacturer but have not heard back yet.
This spring I used the product on the lawn. Must have had wind carry the stream onto the house because multiple patches of yellow blotches appeared on the white vinyl siding. Very unsightly. The product label says “may stain light coloured siding”. Did it ever. Nothing I have tried has worked. In fact it appears to have permeated into the vinyl material. Short of solvents that would damage the vinyl I think every chemical and abrasive combination has been tried. I would rather not replace the siding and use some elbow grease to tidy up the mess.
Any suggestions? Thank you.

Wilson’s MossOut has ferrous sulfate as its primary active ingredient. It is possible you have the equivalent of rust staining on your siding. If you haven’t already, you might try Iron Out, CLR, or a paste or solution of oxalic acid to strip the iron off or out of the vinyl.

As I understand it the culprit is in fact ferrous sulfate. I will try your suggestions. Upon further review the stains are rust-like in colour.
Thank you