Why won't my music USB play in my truck?

What is your question?

I have a 2013 GMC Sierra 1500 SLE and put some music on a 3.73 GB USB, plug it truck and pops message up " can not read ". I can plug my iPhone 6 in, with MP3 cord and MP3 slot, stream Pandora etc., but won't play USB. It is formatted FAT32, don't know why, and internet gives no details as to why it is not compatible.

How long has your 2013 GMC Sierra 1500 had this problem?

Just now trying this.