My mom has been having this problem for around a week or two where she can’t send iMessages to one of her friends. It’ll make that “whoop” sound, but it won’t show delivered. I tried texting her (my mom’s friend) and it works on my phone so it definitely has to be a problem on my mom’s side. She also can’t call her (normal calls and FaceTime audio), it’ll either say FaceTime unavailable or go straight to voicemail. Does anyone know what could be causing the problem? We’ve already tried signing out of iMessage, restating the phone, deleting the iMessage conversation.