ARM InvalidTemplateDeployment: Required property '$schema' not found in JSON - azure-devops

Question

I receive the following errors when attempting to deploy an exported Azure Resource Template:
"The template is invalid. Error: 'Required property '$schema' not found in
JSON.
"Domain name is already taken"
Error Content:
The error content is as follows:
{"code":"InvalidTemplateDeployment","details":[{"code":"DeploymentPreflightValidationFailed","target":"/subscriptions/<SOME_GUID_VALUE>/resourceGroups/<SOME_RESOURCE_GROUP_NAME>-Resource/providers/Microsoft.Resources/templateSpecs/<SOME_ARM_TEMPLATE_NAME>/versions/0.0","message":"The
template is invalid. Error: 'Required property '$schema' not found in
JSON. Path '', line 1, position
2.'"},{"code":"BadArgument","message":"Domain name is already taken"}],"message":"The template deployment
'Microsoft.Template-20220817090827' is not valid according to the
validation procedure. The tracking id is
'c27e8ad4-6d96-46e9-92ed-ac8d5f462bf6'. See inner errors for
details."}
Observations:
I have observed the following:
The latest schema path appears to match what I have listed.
Template:
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"vulnerabilityAssessments_Default_storageContainerPath": {
"type": "SecureString"
},
...
}

Answer 1

The error regarding the $schema property is not referring to the $schema of the template itself, but is instead coming back from preflight (validation) of one of the Microsoft.Resources/templateSpecs/versions resources in your template.
I can repro this myself with the following file I exported (note that Export is stripping out the contents of mainTemplate, which I believe is the root cause of the issue, as it doesn't contain the expected $schema property).
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"templateSpecs_asdgasdg_name": {
"defaultValue": "asdgasdg",
"type": "String"
}
},
"variables": {},
"resources": [
{
"type": "Microsoft.Resources/templateSpecs",
"apiVersion": "2022-02-01",
"name": "[parameters('templateSpecs_asdgasdg_name')]",
"location": "centralus",
"properties": {}
},
{
"type": "Microsoft.Resources/templateSpecs/versions",
"apiVersion": "2022-02-01",
"name": "[concat(parameters('templateSpecs_asdgasdg_name'), '/v1')]",
"location": "centralus",
"dependsOn": [
"[resourceId('Microsoft.Resources/templateSpecs', parameters('templateSpecs_asdgasdg_name'))]"
],
"properties": {
"mainTemplate": {}
}
}
]
}
My team at Microsoft owns the Export Template API - I will follow up internally on this.