The module azure_rm_virtualmachine has fields for plan information. Module azure_rm_virtualmachinescaleset needs to have them and forward them when creating a VM with an image that requires plan info to be specified. The CIS hardened images from the Azure Marketplace is a prime example.

description:
            - Data which is made available to the virtual machine and used by e.g., C(cloud-init).
            - Many images in the marketplace are not cloud-init ready. Thus, data sent to I(custom_data) would be ignored.
            - If the image you are attempting to use is not listed in
              U(https://docs.microsoft.com/en-us/azure/virtual-machines/linux/using-cloud-init#cloud-init-overview),
              follow these steps U(https://docs.microsoft.com/en-us/azure/virtual-machines/linux/cloudinit-prepare-custom-image).
        version_added: "2.8"
extends_documentation_fragment:
    - azure
    - azure_tags
author:
    - Sertac Ozercan (@sozercan)
'''
EXAMPLES = '''
- name: Create VMSS
  azure_rm_virtualmachinescaleset:
    resource_group: myResourceGroup
    name: testvmss
    vm_size: Standard_DS1_v2
    capacity: 2
    virtual_network_name: testvnet
    upgrade_policy: Manual
    subnet_name: testsubnet
    admin_username: adminUser
    ssh_password_enabled: false
    ssh_public_keys:
      - path: /home/adminUser/.ssh/authorized_keys
        key_data: < insert yor ssh public key here... >
    managed_disk_type: Standard_LRS
    image: