If you deployed your API management instances in virtual networks, please continue reading the following.
We have switched from port 443 to 3443 for the management endpoint for Azure portal and PowerShell (see this documentation or the table below). The change allows customers to segregate and control inbound management traffic. On June 1, the management endpoint will no longer support port 443. Therefore, to ensure configuration management experience for your service continues to work properly after June 1, please make sure port 3443 is open for the inbound direction.