OPA - rego policy to validate RBAC with Azure Key vault

Question

I am new to OPA and want to add some OPA policies with my Terraform deployment pipeline. Here are the code that I use for validating with OPA policy. But the result.json is empty. Which means the policy is not functioning.

package terraform.keyvault

 Allowed roles for administrators
admin_roles = {
    "Owner": true,
    "Contributor": true
}

# Ensure the assigned role is allowed for managing Key Vault
valid_admin_role_assignment[assignment] {
    assignment := input.planned_values.root_module.resources[_]
    assignment.type == "azurerm_role_assignment"
    role := assignment.role_definition_name
    admin_roles[role]
}

# Invalid admin role assignment (when a user is assigned a non-admin role)
invalid_admin_role_assignment[assignment] {
    assignment := input.planned_values.root_module.resources[_]
    assignment.type == "azurerm_role_assignment"
    role := assignment.role_definition_name
    not admin_roles[role]
    print("Invalid admin role assignment:", role)
}

I have tried to get the value to debug using the below code. But this also results an empty json.

debug_assignment[msg] {
    assignment := input.planned_values.root_module.resources[_]
    assignment.type == "azurerm_role_assignment"
    msg = sprintf("Assignment: %v", [assignment.role_definition_name])
}

Any help would be appreciated.