Got "Failed to upload thumbnail asset." when trying to submit the template to Vercel

I am trying to submit a template to Vercel by using Vercel Template Submission Form. And I always got an error like

{
    "error": "Failed to upload thumbnail asset."
}

from Vercel's service response. And I don't know what's wrong or Vercel doesn't receive the submission for now. Here is my repo: LikeDreamwalker/nextjs-mui-zustand-template: Best practices with next.js, mui and zustand. And here is my thumbnail image link: https://nextjs-mui-zustand-template.ldwid.com/images/demo-thumbnail.png I tried multiple ways by using Github's CDN, or the Vercel itself, but always got this issue so I think this might not be related to the image itself. By the way I will always got a error response if the image is above 100kb, and this image is now under this limitation.

I am trying to submit a template to Vercel by using Vercel Template Submission Form. And I always got an error like

{
    "error": "Failed to upload thumbnail asset."
}