Easiest way to reproduce this is to go to the official documentation at:
Essential Studio for Angular > Data Grid > Editing > Inline Editing
The sample on that page works, but only because the page is using Angular 6.1.10.
If you click the "Edit in StackBlitz" link, it will bring the sample up using Angular 9.1
Wait for the devServer to start and then simply double click to edit a row in the data grid. Then click on the "Ship Country" column (which uses editType='dropdownedit').
You will get a message "The Request Failed"