How to select a sub-string during the Property Transfer?

Hi guys,

I'm pretty new of SoapUI and I'm trying to learn more possible and read documentation but I'm stuck with the following problem:

In SoapUI I create a Test Case with multiple test steps and a sub-string of the first API response should be as input of the second API call.

In property Transfer I have the following JSON Path:

$[?(@.name == ComputeResource)].url[0]

and the result is something like [http://........../......../1548356546]

The problem is that I want transfer only 1548356546 and not all the string, I try different way to transfer only the sub-string part interested but I get every time an error....

like this one: [java.lang.String cannot be cast to java.util.List]

Can someone help me?

Thanks so much