There can be a few reasons as to why you can't upload a file.
Have a look at below points and check if any of them resolve the issue.
The file you're trying to upload is too large. Maximum size (per file) is 20 MB.
You need to upgrade your price plan with more storage. Reach out to us at customercare@careofcrm.com and we'll help you with the upgrade.
There's always 0,5 GB storage included in all price plans for storing documents and emails.