Hi:
It could be failing for several reasons, and it will be difficult to diagnose. Let's start by cleaning out all the crud from your old configurations.
Log onto the OBiTALK web portal, where you set up your OBi 200. Click the SPx (SP1--4) where you configured Google Voice, and delete that configuration by clicking the trash can to the right. Wait a few minutes until the OBi's LEDs start blinking, and then stop (except for some minor flickering on the middle LED).
Leave that web browser tab open. Press Ctrl-T to open another browser tab. In that second tab, sign into the correct Google/Gmail account that holds your Google Voice number:
https://voice.google.com/settingsConfirm that you see your Google Voice inbound number at the top of the web page. If not, then you're signed into the wrong Google account. If so, then look carefully at the list of linked phone numbers. Delete all linked phone numbers that you no longer control (abandoned/canceled service). Scroll down to the "Calls" section. Temporarily remove the check marks next to all of your linked forwarding phone numbers, so that calls will not be forwarded to them.
Now, go to this page:
https://myaccount.google.com/. See the first screenshot below, and click on "Apps with account access". On the next page, click the blue "MANAGE APPS" link. On the next page, delete all the third-party apps shown in the second screenshot below. Don't close the tab. Go back to your Google Voice web page in that tab.
Go to the other tab, open to OBiTALK. Click SP1 or whichever SP you want to use, and set up Google Voice again. After it is finished setting up, and it says "Connected", then make some inbound calls to your Google Voice number, and/or enlist some friends or family to do the same, preferably from other carriers. The expected behavior is that your OBi-attached phone should ring every time. Does that work? If not, report back exactly what happens.
If it does, work, then go back to Google Voice settings and re-enable your forwarding phone number(s) by adding check marks. Retest. If it fails now, it is because one of your forwarding numbers is interfering.