Problem with DRTLS_Manager_source_R2


I am currently working on the Source code for the Android application DRTLS but I am facing with a problem.
In fact, I want to build APKs as described in the READ_ME.docx but I have a lot of errors.
I get a “Connection timed out: connect”.

13:38 Gradle sync failed: Connection timed out: connect (4 m 24 s 396 ms)

13:38 Syncing only active variant
You can disable this experimental feature from
File → Settings → Experimental → Gradle → Only sync the active variant

I don’t know how to fix it.

Moreover, when I cliked on Build->Build APK(s), nothing happened…

Could you help me please ?