Welcome to OBiLand. The no-inbound-call symptom can have several causes. The typical cause is that you authorized the OBi device to use the wrong Google account: an account that doesn't have an inbound Google Voice number.
Use a laptop/desktop computer, not a tablet or phone. Open a browser window. If you're using Google Chrome Browser or Safari, press Ctrl-Shift-N to open an incognito browsing window, or, if you're using Firefox, press Ctrl-Shift-P to open a private browsing window. Using that window sign into the one and only one Google/Gmail account that you used to set up your Google Voice phone number, and go here:
https://voice.google.com/settings.
Do you see your Google Voice number at the top of the page, under "Account"? If not, it's the wrong account, or you didn't set up a number. If you do see the number, then, still in that incognito/private browsing session, press Ctrl-T to open another browser tab. In that tab, go to your OBiTALK dashboard:
https://www.obitalk.com/obinet/.
Click on your device to go to its main configuration page. Click the trash can to the right of the SPx you set up with Google Voice and wait a few minutes, watching while your device reboots. After it's stopped gyrating, then click the SPx again, and set up Google Voice. This time, make darn sure that the account that it asks for your permission to use is the same account with the Google Voice number. Complete the procedure and then call the number from some other, unrelated phone number, not another GV number, and not a number you linked as a forwarding number. What do you, as the caller hear, exactly? Does it ring the OBi-attached phone? Does the Phone LED on the OBi device blink while you, the caller, hear ringing? If it rings, can you answer the call?