You want to know why this button disappeared
You want to know how to do synchronization
SAP Business ByDesign
After 2108 veriosn,the button "Master Data Synchronization" has removed from the view "invoice scanning". instead its visible under "application and user management"work center.
Refer the screenshot attached to this KBA as to where you can see this option under Application user management.
Synchronization is happening automatically after 2108 version, Thus button is moved from scanning screen cause you don't have the need to use it frequently.
Every day job will run in the night in CET time mostly to do the synchronization, however if you want to forcibly do the synchronization then you have to go to application user management work center and do the synchronization.
KBA , AP-SIP , Supplier Invoice Processing , Problem