In this case where you cannot add the service-worker.js file to root folder.


You will have to change your subscription dialog box from Push Single Step opt-in to Safari or any other. 


We suggest you can try out Safari style box, for this you can navigate to Settings > Subscription dialog Box settings > HTTPS > Safari Style Box > Edit > Configure > Save and Publish. 


Please contact care@pushengage.com if you have any more questions.