Sharing a file via the chat

Hello: I am running latest IOS on MacBook Air. Using Canvas and Zoom in side Canvas, but also often just use the separate Zoom APP on my Mac. For some reason, during classes, I simply cannot share files via the chat anymore. Why not? It used to work just fine. Drag and drop - no issues. Suddenly this is a problem. I have looked EVERYWHERE for an answer but find no advice and no setting adjustment that will fix the issue. Anyone who can help will be much appreciated since this is having an adverse effect on my classes now. Thank you