Configuring SharePoint File Storage "ACCESSDENIED"

Can someone please assist me in configuring sharepoint for our Sales Orders Attachment storage? We are trying to save them to our sharepoint site, but I keep getting and access denied error. I found a post on here to put SPLogonMode in the sysconfig file and set it to interactive, but I still do not receive the logon window to enter my 365 credentials. I put this in the app settings section, is that the right/wrong spot? Is there a step by step pdf somewhere that would walk me through this? I have tried the address with and without sites as well, same error. Thanks for any help, it’s greatly appreciated!!

Did you ever find a resolution?

Yes, it wasn’t fully implemented in our version. We went with local storage and will move to SharePoint cloud when we finish this upgrade.