You have to fix the problem that the error message is telling you, before you can expect anything else to work.
The OBiTALK portal has been a complete mess recently, so whether or not it's a legitimate problem needs further investigation by you.
It's telling you that the OBiTALK device you're trying to use is not assigned to an OBiTALK portal account. You need to sign into the correct OBiTALK account and successfully add the device to the dashboard.
Since you are working with multiple Google/Gmail and perhaps multiple OBiTALK accounts, web browser cookies can cause confusion as to which account is being accessed.
Using Google Chrome Browser, Microsoft Edge (Chromium) or Safari, open the browser, then press Ctrl-Shift-N to open an Incognito browsing window. If you're using Firefox, press Ctrl-Shift-P to open a Private browsing window. Use that window, sign into the correct Gmail account that now holds the Google Voice number, and go here:
https://voice.google.com/u/0/settingsDo you see the Google Voice phone number at the top of the page? If not, this is the wrong Gmail account. Close and re-open the Incognito/Private browsing window and try another Gmail account until you find the correct one. Assuming that you've now found that account, leave that window open.
Do NOT sign into more than one Google/Gmail account in this browser window. If you need to change accounts, close and re-open the window.
Press Ctrl-T in the Incognito/Private window to open another browser tab. Sign into your OBiTALK portal account. Is the OBiTALK device listed here?
http://www.obitalk.com/obinet/pg/obhdevAgain, if you don't see the device listed, you need to fix that.
Once you finally have the window open with two tabs, one with the correct Google Voice number's configuration page, and one with the correct OBiTALK page, then add Google Voice to the device's SP1 service provider.