co-authoring in excel-issues

Hi guys,

I'm Adrian and i have few issues with co-authoring in excel, the steps that we done are:

1. I copied a excel file to One drive for business(simple file, without any data validation or pivot tables etc). We have office 365.
2. we were able to connect to this file all the teams in same time and we were able to write in this file but only if we chose Excel for web. for excel desktop we are receiving the message "read-only".
my first question is-why we are receiving this message?is there some settings that must be done?
3. we are fine to work in excel for web...but...if we tried to work in a file with data validation we received the message that is not supported.
i read a lot on forums, and i saw that data validation is supported by excel for web(maybe not all the versions).

can you please advise what's missing? some settings/rights? i'm not a technical guy so if you can give me some details(are missing some settings in sharepoint/one drive for business? or maybe we have some internal restrictions?)

thank you!