@Louinord Innocent like Luke mentioned above, can you provide more details on the error you are getting so narrow down the cause of this issue?
In the meantime, I would recommend you double check to make sure you have a valid Azure Communication Service resource created in your Azure subscription and that you've correctly copied the connection string (endpoint and access key) from the Azure Communication Service resource to your WordPress application settings.You also need to verify that your WordPress site is configured to use the Azure Communication Services Email plugin for sending emails.
Even if the activation email isn't being sent, try sending a test email from your WordPress site using the plugin's functionality. This can help isolate if the issue is with activation or general email sending.
Hope that helps.
-Grace