Why strapi only allows user email as user id not the username we configured?

System Information
  • Strapi Version:
  • Operating System:
  • Database:
  • Node Version:
  • NPM Version:
  • Yarn Version:

in Settings> users> invite a user> ,

fill out both user email and username, I thought both of them can be used as userid interchangable, is there anything missing in the implementation?