For each request they give one slot to upload, so they expect one document. I think the passport pages are quite rare for them to have uploaded. They could word it better to ask for a copy of all passport pages in a single PDF.
We have to remember this is Thailand and not everything is simple 😂
Each time you upload you overwrote what you already sent. You need to combine all the pages into one pdf. All pages of passport into one single document.