I would recommend to check from the local gateway appliance if all API endpoints are properly reachable. To do this you need to connect to the local console of the gateway, e.g. via the ESXi management console or via vCenter. After you login (the default credentials are admin/password, please change the password if this is still the case) you can select option 3 from the menu: Test Network access.
Depending on your chosen setup it lists either the public or VPC endpoints the gateway needs to connect to.
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