No problem, basically aim to remove all reference to previous syncing attempts at both "ends" ie. on phone and car, because anything remaining could be "interferring" with the subsequent re-syncs attempts.
I also suggested a Force Restart of the iPhone because that is a standard fallback when the device gets a little glitchy, a bit like restarting your Mac.
If you still can't get the sync to work correctly, I would drive to your dealer, or if they are too far away another BMW garage, because someone should be able to help or may have come across this issue, just because one garage doesn't know doesn't mean another won't, even some car audio specialists may be worth a try if they are local.
Just a few thoughts, best of luck.