Please note that if you have a work or school account, you might not have a version of Office that supports co-authoring yet.
Forum Discussion
Not able to have all users be in the same excel file at the same time in Sharepoint
I have a excel workbook with a pivot table in it and some macros, nothing too crazy. I enabled Sharing to allow all the team to be in it at once. It does not seem to be working when i am in it it giv...
You do not need to use Excel online to co-author, you can use Excel local client or Excel mobile, but it has to be from an Office 365 tenant login. I assume the file is in .xlsx format? So the issue you're asking is that you want users to be able to co-author, but its not and instead users are getting the "file is exclusively locked by X user" message? Is this file stored in a SharePoint document library? How are you opening it? From the library, or from Teams, or other? Give this a glance and see if it helps, it even has a section about the file locked error:
https://support.office.com/en-us/article/collaborate-on-excel-workbooks-at-the-same-time-with-co-authoring-7152aa8b-b791-414c-a3bb-3024e46fb104
There are constraints though: https://support.office.com/en-us/article/collaborate-on-excel-workbooks-at-the-same-time-with-co-authoring-7152aa8b-b791-414c-a3bb-3024e46fb104Collaborate on Excel workbooks at the same time with co-authoring - Office Support