I've just tried attaching a file from my OneDrive to a Trello card, but nothing seems to happen. The steps I took were as follows:
1. Add OneDrive Power-Up to board
2. Open card and select OneDrive Power-Up
3. Follow prompts to link OneDrive account via pop-up modal (taken to Microsoft sign in page).
4. Click on OneDrive Power-Up again
5. Select "Attach a File"
6. Modal appears with all my OneDrive files
7. Select word document and then click "Select"
8. Modal disappears
Result: No attachments are added to the card
