Multiple precompiled assemblies with the same name. Only one assembly with the same name is allowed per platform

it happenes when I import Facebook SDK in the project.

I previously used unity 2019.1.6, then I updated to 2019.1.9 thinking it will make the problem go away. but no.

I have already tried.

1 - remove unity.ads from package manager.

2 - removing ad package from \Packages\mainfest.jason file

these are the only solutions I could find on the internet, but none worked. please help.

reset Ediot Layout to Default

https://forum.unity.com/threads/editor-error-after-update.598330/