@Madusha Mihiran , that site doesn't currently resolve, so if you want it, then you should create the app service now. With regards to your question, yes, app names need to be globally unique due to the fact it will DNS resolve to app-name.azurewebsites.net
. This is regardless of which Azure tenant you're using/signed in to.
As to the possibility of this type of scenario, the only thing I can think of is it already existing and the owner of that site deleted it.