Products must exist first because an RFID tag only gives the system an EPC. The tag does not know the item name, size, color, price, or warehouse by itself.
In Easy Inventory, create or import the catalog first, check SKUs, variants, assigned warehouses, and sale status. Then apply tags and link each EPC to the correct SKU or variant.
Common mistakes are using one SKU for many sizes, tagging before the catalog is clean, or allowing duplicate SKUs. Those mistakes make Stock In, Stock Out, Inventory Count, and POS all operate on the wrong item.