Hi AndyMercury,
Welcome to the Apple Community.
Wondering which device, or PC, Mac, you are using, and which Operating System is installed on it.
You might want to browse these articles from Apple Support.
What happened to iTunes?
https://support.apple.com/en-us/HT210200
If you can't open the App Store or iTunes Store, buy content, or edit payment information:
https://support.apple.com/en-us/HT208104
Set up and view an iTunes Store account in Music on Mac
https://support.apple.com/en-au/guide/music/mus46db3a1a/mac
Intro to the iTunes Store in Music on Mac:
https://support.apple.com/en-au/guide/music/mus3e2346c2/1.1/mac/11.0
iTunes User Guide
https://support.apple.com/en-au/guide/itunes/welcome/mac
iTunes Support
https://support.apple.com/itunes
iTunes Support. Worldwide
https://support.apple.com/choose-country-region/itunes
Hope something here smoothes the way for your song purchases :-)