I CAN'T UPLOAD MORE THAN ONE PDF TO KNOWLEDGE

I've tried many times uploading, but it loads for a really long time only to keep saying, “Ensure your connection is stable and try again”. Of course I looked if it was truly a network issue but everything is fine on my end! Please help me fix this issue immediately because I'm in a real hurry to study for my exams next week. I have already paid for the service so I would appreciate swift response