Due to new corporate policy that allows us to track airplay and properly pay music royalty fees, we are required to have an ISRC code for any song that we play on the radio. We (and any streaming service) cannot play your song without one. There are several ways you can acquire an ISRC, but the easiest way is through an aggregator like Tunecore or CDBaby. These services will charge around $10/year per song but will allow the artist to publish & sell their work on iTunes, Amazon, Spotify, etc. Another option is to just buy the code. There are several 3rd parties selling codes – search to find one that works for you. iHeartMedia does not endorse or favor any particular service.
Here is a link to more information from the International Standard Recording Code and how to obtain: https://www.usisrc.org/applications/faqs.html