Web recorder not starting

HI, I gave url of app, but web recorder is not starting!
I am first time user and it gives me following reason. I am not a programmer, how can I resolve this issue???

Reason:
com.kms.katalon.core.exception.StepFailedException: Unable to open browser with url: ‘’
at com.kms.katalon.core.webui.keyword.internal.WebUIKeywordMain.stepFailed(WebUIKeywordMain.groovy:64)