Unfortunately, there appears to be an issue with your specific account.
You should be able to activate the service from My Verizon portal using these instructions inputting (559) 533-5694 in "when my line is busy" box:
After completing these steps, go back to the app and try to activate the service.
If you were unable to activate the service, we recommend calling Verizon Technical Support and stating the following:
1. "I am unable to activate conditional call forwarding on my number. Dialing the star nine zero (*90) activation code does not work. Can you activate my conditional call forwarding for me? I want it to forward calls when busy"
2. When they ask what number you would like your calls forwarded to, give them this number: (559) 533-5694
- Please don't mention Assistant, your carrier might state that they do not support third-party applications as a way to avoid dealing with the request.
- If the representative is unable to help you, ask to speak to another representative or supervisor. Do not let them tell you that they can't activate conditional call forwarding. Call forwarding is a carrier side setting and only they can get it activated
Verizon Customer Support