The reasons why the signature of the contest failed to upload are: incorrect file format, file size exceeding the limit, and network connection problems.

The format of 1. file is incorrect: the signature file must be in JPEG or PNG format.

2. The file size exceeds the limit: the size of the signature file cannot exceed 2MB.

3. Network connection problem: when uploading the signature file, a stable network connection is needed, and the unstable network will lead to the failure of uploading.