Azure InvalidTemplate Error: The language expression property array index '1' is out of bounds.

I'm trying to spin up a Redis Cache in Azure and placed it in my Virtual Network. However, it threw an error and the error message was not helping but I eventually figured it out.

Here's my Bicep template which threw an error:

resource cacheSubnet 'Microsoft.Network/virtualNetworks/subnets@2023-11-01' existing = {
name: 'mySubnet'
}

resource redis 'Microsoft.Cache/redis@2023-08-01' = {
name: 'myRedis'
location: resourceGroup().location
properties: {
enableNonSslPort: true
publicNetworkAccess: 'Disabled'
sku: {
capacity: 1
family: 'P'
name: 'Premium'
}
subnetId: cacheSubnet.id
}

Apparently, I needed the parent field on the subnet reference, so I ended with the following template which successfully launched my Redis cache.

resource vNet 'Microsoft.Network/virtualNetworks@2023-11-01' existing = {
name: 'myVNet'
}

resource cacheSubnet 'Microsoft.Network/virtualNetworks/subnets@2023-11-01' existing = {
name: 'mySubnet'
parent: vNet
}

resource redis 'Microsoft.Cache/redis@2023-08-01' = {
name: 'myRedis'
location: resourceGroup().location
properties: {
enableNonSslPort: true
publicNetworkAccess: 'Disabled'
sku: {
capacity: 1
family: 'P'
name: 'Premium'
}
subnetId: cacheSubnet.id
}