Hi,
To transfer to different registrar you will need authorization code. You may open Azure Cloud Shell and execute command similar to below from App Service team blog (replace subscription id, resource group, domain name):
Invoke-AzRestMethod -Path "/subscriptions/<SUBSCRIPTION-ID>/resourceGroups/<RESOURCE-GROUP-NAME>/providers/Microsoft.DomainRegistration/domains/<DOMAIN-NAME>/transferout?api-version=2021-02-01" -Method PUT
In the output from the command, you need authCode, which is what you will provide the new domain registrar when requesting transfer in.
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Thanks.
-TP