You need to contact Wave
Although "Call Forwarding No Answer" and "Call Forwarding Busy" are typically included in your Wave Business phone package at no additional cost, there is not a way to turn it on yourself from the web or your phone.
You can contact Wave Business using web chat or by phone. If you have it handy, you may want to grab the account security PIN from your billing statement, as they may use that for verification.
Web chat: Visit https://business.wavebroadband.com/smbvoice/ and click on the chat button in the lower left hand corner.
Phone: Dial 1-844-910-8519.
When you connect with Wave support, tell them you want to enable BOTH "Call Forwarding No Answer" and "Call Forwarding Busy" on your business phone, and in both cases have them forward the calls to the "Numa Number" assigned to your Business location.
How to Confirm It's Working
You can place a test call by going to Settings > Phone numbers > Test my setup or call your business's phone number from your personal phone. If nobody answers, you should hear your Numa Voicemail greeting.
To Disable Call Forwarding
To disable the call forwarding, you will also need to contact Wave (using the same methods as above).
Make sure you don't have an answering machine picking up your calls before they get forwarded.
If your business's phone line is part of a hunt group (multiple lines that ring until one is answered), you may need to set up forwarding on all the lines involved. Alternatively, you could remove your business phone line from the hunt group.
Contact your phone provider and have them double check that forwarding was set up properly and is active on your line.
No matter what, don't hesitate to contact Numa support! We'll happily work with you and your service provider to get you all set up.