we are trying to add Excel files for shared use amongst team members so we can collaberate

[David Masi]

Uploading working excel files so we can have multiple folks working at the same time

[Jack Brickey]

So while you can certainly attach an excel file to a Jira issue it cannot be collaboratively edited (simultaneously) by users. Attachments are snapshots and as such would have to be downloaded, edited and attached again. Likely opting to remove the original. Options include:

• Use confluence and tables
• use a link in the issue to say a Sharepoint file that support concurrent editing
• use Teams 
• look at various excel addons in marketplace