Upload Failed (-1) while trying to upload a world to Realms

Trying to upload an old world that weighs about 0.8GB to our realms server, it's getting consistently stuck at around 5% or 6% when uploading (Error "-1"). This is really odd to me and I have just paid for the membership. I need help, we can't start another world because this one is very important.

 

I already tried on two PC's, both of which have Minecraft Java Edition (Win 10). I have seen many error 500's online but not a single error "-1". Help!!!