@Marcel Croes (DutchWorkz BV) Thanks for reaching here!
This is due to new feature App Service recently (14th Nov 2022) rolled out a Name Reservation feature to protect customers from the threat of subdomain takeovers.
This new built-in feature creates a name reservation for web application names. No additional changes or configuration are needed by the customer to establish a name reservation.
The name reservation for a given resource name will exist from the moment the resource is created and for a lengthy time period after the resource has been deleted (a cooldown period). This means that during the cooldown period after resource deletion, other subscriptions outside of the original creating Azure AD tenant will not be able to create a web application using the same name.
However, once the cooldown period has ended, the name reservation will be released, and any subscription will then be able to create a web application with that given name.
Note that the length of cooldown period is determined by the quota id of the subscription that previously owned the reservation. If your quota ID is enterprise or CSP its around 180 days but for others its around 7 days.
See: Name Reservation on App Service for Web Apps and App Service Environment (ASE)
Resolution:
Option 1: You can wait for the cooling-off period to expire (unless it was previously used by an internal subscription).
Option 2: Please reach out to us by sending an email with subject line “Attn:Sneha |thread title” to AzCommunity[at]microsoft[dot]com referencing this thread.
Hope this helps.