Only thing to do is to check your account and make sure that number isn't being block by spam protection. Sign into your account on Visible, click on the privacy and security tab, look at recent auto-blocked calls, also check report a recent caller, there also may be a number there. If there is a number in either of these two location I don't know how to remove or make the number a safe caller number, I have never changed one. Another thing is if you have spam protection turned on for your line what are the settings? If you have spam protection turned on tap on edit filter settings and see if you have it set to block completely in the right column. If you have it set to that and the number from your friend is thought to be a spam call the person calling, from my understanding, won't be able to leave a voicemail and you won't hear it ring.
The left column for settings is a little hard to understand, if you have it set to high risk only number that are known to be spam or are considered high risk will only be blocked. But if you have it set to all spam this could also flag numbers. Not sure but I think this flagging can be if another person(s) have reported the number as spam. I have mine set to all spam and voicemail.
Also, this is a peer to peer forum and we can only suggest what to try, if there is another issue like the person getting an error message while calling your number then you would need to know what the error message says or what is happening when the person calls and then contact Visible customer service and see if they can fix the issue.
