When a user selects the ETV service from an IP Phone, it sends out a HTTP request to the DMM server. So before starting, we should rule out the possibility that the DMM server is actually unreachable. Try pinging the DMM from another computer on the network. If you are not able to, then make sure that the DMM is running and connected to the network. If the DMM is reachable, please check the setting for ETV service in the CallManager. To do this, follow the steps below:

Log into the CallManager
Go to ¿Device > Device Settings > Phone Services¿
Click on the ¿Add New¿ button
Fill in the Service Name, Service URL, Service Description and click on the Add button
           Service URL example - http://<DMM_IP>:8080/etv-remotecontrol-webapp/app/getpin
Go to ¿Device > Phone¿ and click on Find button to list all of the registered phones
Click on the desired phone link to bring up the Phone Configuration page
Select ¿Subscribe/Unsubscribe Services¿ from the pull-down list ¿Related Links¿ on the upper right-top corner
Click on the Go button next to the pull-down list
Select the service you just created for ETV from the pull-down lists ¿Select a service¿
Click on the Next button for the next page
Click on the Subscribe button, and then the Save button
 
let me know if after trying this, you are still unable to resolve your issue

Thanks,
-Hashir

You see the pin prompt because you configured a URL to ETV that requires the user to input a  pin.

If you just want to control an HTML application, you should not fill in the DMM server¿s ETV URL. You should use your own URL. To do this you will need to make the following change:

Fill in the Service Name, Service URL, and Service Description and then click on the Add button
i.e. Service URL sample: http://<Your_URL_Here>

This is not related to the DMM. Just configure a service from the Call Manager and deploy it to the ip phone.