Update SharePoint Online items from outside of SharePoint using the SOAP / XML API


We need to update SharePoint Online list items from a standalone application outside of SharePoint by an outside company (CRUD).

This application uses soap / XML calls to call SP.

The (external) application could easily connect and update a local SharePoint 2010 list. Now we are migrating to SharePoint Online.

The external application can connect to and display list items but always throws an error when we try Refresh an item in the list on SharePoint Online

Here is the (edited) soap requirement body and the answer:


   
   
      
         XXXXXX GUID
         
            
   
      1002
      1
      RL101150
      2020-03-03
      andras boros
      
      This is Box 20/1
   
   
      1003
      1
      RL101151
      2020-03-03
      andras boros
      
      This is Box 20/2
   
   
      1004
      1
      RL101152
      2020-03-03
      andras boros
      
      This is Box20/3
   

         
      
   

4:02

   
      
         
            
               
                  0x81020026
                  The list that is referenced here no longer exists.
                  
               
               {TL:DR}
             
            
        
    

Is it possible to update SharePoint Online list items from a standalone web application to a completely different document?

And how would we deal with authentication?

Any help on this would be greatly appreciated.