If you are facing the Gmail Error 400, it might be due to the settings in the chrome, Content settings and many more, If facing the same issue, again and again, try to resolve it by following all the guidelines.
For deleting the Gmail-imp file do a right-click on your error screen.
After that click on ‘Inspect Element‘ and open the developer window, it ‘Inspect Element’ visible on the bottom of the open tap.
Once the developer window appears, click on the ‘Application‘ tab which you can see top-right of the developer toolbar.
After that, choose the clear storage from option, which appears the below of Application.
When you click, on the right side a new tab was open, from the tab option select the below options ‘Cookies‘ ‘Cache storage‘ and ‘Application cache‘.
Once you select from the options, click on ‘Clear Site Data‘, this will clear all the saved cookies from the Gmail page.
After that close the developer window and refresh the page.
Check the Submitted URL. Clear Browser Cache. Clear Browser Cookies. Check if File Upload Exceeds the Server Limit. Clear DNS Cache. Deactivate Browser Extensions.