Tried to book on DL.com for DD Daughter and a friend from PNS-HNL. Got flights I wanted, went to pay and clicked to use CC in profile. Get "We cannot bill this credit card. Please use another card." Knew the CC was good, so tried it twice more and got the same message. Switched to MrsDD's CC and got the same message. Switched to MrsDD's SM# and tried both cards and got the same message.

Finally, went to Orbitz, booked flights with my original CC and got the confirmation email within 3 hours. Went to DL.com to verify itinerary and there it was. I don't know if it costs Delta anything for Orbitz to book their flights, or not, but it was a pain.