Why I can not attach my documents in Trello?

[Winny]

When I want to attached the document it shows exclamation mark and uploading file…

[Michael Yaroshefsky - Visor for Jira]

Hi @Winny

Welcome to the Atlassian Community.

There could be a few reasons why you can't upload attachments and you're seeing the exclamation point.

1. Unsupported file format. Double check you didn't use a file format Trello doesn't support.
2. You exceeded the file size. Trello has file limits for free accounts (10MB), and for paid accounts, the limit is 250 MB.
3. Trello may have gone down temporarily. If any incidents were reported with viewing and loading attachments, you can view them here: https://trello.status.atlassian.com/

For further reading see this support article https://support.atlassian.com/trello/docs/adding-attachments-to-cards/