How do you ship your orders to Amazon? Via Poslaju or some other 3PL that you've signed up with?
You need the FDA cert,Lab test and etc, too complicated.
I sourced my products from China and my agent shipped it directly to Amazon warehouse.
She does the labelling, inspection and packing for a fee.
You need to watch alot of youtube videos on Amazon fba, watch atleast 2 -3 videos daily on that subject.
Do this for 2-3 months. Then you will get the general idea