Value for reference id is missing. Path properties.ipConfigurations[0].properties.publicIPAddress

I'm trying to deploy a Virtual Machine using an ARM Template. The VM needs to have a static IP address. When deploying the template I'm getting an error. I think I'm getting the reference to the public IP address from the network interface wrong but I can't see how I should do this? The error is:

20:13:01 - The deployment 'my-template' failed with error(s). Showing 1 out of 1 error(s).
| Status Message: Cannot parse the request. (Code: InvalidRequestFormat) - Value for reference id is
| missing. Path properties.ipConfigurations[0].properties.publicIPAddress. (Code:MissingJsonReferenceId)
| - Value for reference id is missing. Path properties.networkSecurityGroup.
| (Code:MissingJsonReferenceId) CorrelationId: ab49b076-8888-8888-8888-8888888888

I've defined the IP Address thus:

    {
        "type": "Microsoft.Network/publicIPAddresses",
        "apiVersion": "2020-04-01",
        "name": "[variables('myVmIpName')]",
        "location": "[variables('location')]",
        "sku": {
            "name": "Basic"
        },
        "properties": {
            "ipAddress": "198.51.100.176",
            "publicIPAddressVersion": "IPv4",
            "publicIPAllocationMethod": "Static",
            "idleTimeoutInMinutes": 4,
            "dnsSettings": {
                "domainNameLabel": "[variables('myVmDnsName')]",
                "fqdn": "[concat(variables('myVmDnsName'), '.', variables('location'), '.cloudapp.azure.com')]"
            }
        }
    },

And the network interface is defined like this:

    {
        "type": "Microsoft.Network/networkInterfaces",
        "apiVersion": "2020-04-01",
        "name": "[variables('myVmNicName')]",
        "location": "[variables('location')]",
        "properties": {
            "ipConfigurations": [
                {
                    "name": "ipconfig1",
                    "properties": {
                        "privateIPAllocationMethod": "Dynamic",
                        "publicIPAddress": "[reference(variables('myVmIpName'))]",
                        "subnet": "[reference(variables('myVnetName')).subnets[0]]",
                        "primary": true,
                        "privateIPAddressVersion": "IPv4"
                    }
                }
            ],
            "enableAcceleratedNetworking": false,
            "enableIPForwarding": false,
            "networkSecurityGroup": "[reference(variables('myVmNsgName'))]"
        }
    }

I've changed some of the definition to protect the innocent, but hopefully it is near enough to show the error.