At this moment in time Splitly only supports sellers who are selling through Seller Central and who have listing control over their products. Listing control means you have privileges to edit the fields in your product listings. Note that sometimes Amazon places restrictions on the title fields. Furthermore, you must have at least a few daily sales each day for there to be enough data to perform an A/B test.
We currently do not support DropShip Central or Vendor Central. We are looking at exploring these opportunities for Splitly further down the line.