ChatGPT Plus not uploading manuscript

I finally gave in and purchased the paid version of ChatGPT. Thomas, on a recent AI podcast, talked about how uploading your entire manuscript to a paid AI model will help organize the editing process. In corresponding with OpenAI (ChatGPT’s mother station), they told me “…uploading your full manuscript as a single file (around 1MB) is entirely feasible—no need to paste content piece by piece.” My novel is under 1 MB. They also told me GPT-4o can “Refine pacing and dialogue authenticity… (and) strengthen emotional beats…” All reasons why I purchased an AI. But I can’t even upload a full chapter. I can barely upload 300 words from Word. If I try uploading more than that, it tells me “The message is too long.” Really? I can upload a full chapter easily on any of the free AI versions. Does anyone know how to work around this problem without having to copy and paste every 300 words? Or should I just give up and use the free versions?