Could you please check if you have swagger plugin installed on your computer before importing Swagger definition?
Also, make sure that you follow the steps listed in this article.
I believe that @turandrey is doing right. Only thing is that SoapUI OS edition does not show the post request for REST Requests like in SOAP Request. May be that is intentional, not sure.
Probably RestAPI would show up the request content for POST methods, give a try.
You absolutely right. I followed all instructions which TanyaGorbunova sent me but unfortunately get same result.