Welcome to TPG Community!
We have located the account using your community details and we can see that you're currently using a TP Link VR1600v modem.
To disable the AP Isolation, you may follow the steps below:
1. Open your browser and in the address bar type http://192.168.1.1 and press Enter.
2. Enter admin for both the username and password and click Login. If you have changed the login credentials, please enter the current username and password for your modem interface.
3. You will see the home screen shown below. Click on the Advanced Tab.
4. Go to Wireless > Advanced Settings page. Locate the AP Isolation section and untick the checkbox to disable the AP Isolation.
5. Click Save to make the settings effective.
Let us know if we can be of further assistance. Thank you.
What error message does it give you? In the event that you're trying to setup a 3rd party cast device we highly recommend to contact the manufacturer for further support to avoid misinformation troubleshooting with the equipment.