Livewire3 Nested Data Binding

I'm migrating an app from Livewire2 to Livewire3.

Livewire2 supported nested data binding. Very brief docs here: https://laravel-livewire.com/docs/2.x/data-binding#nested-binding

This meant that you cold feed a model into a component and then access and update all the model attributes without having to explicitly bind and declare each attribute.

So for instance, you could call a component:

@livewire('invoices.invoice-customer-details', ['invoice' => $invoice])

And then in the component just declare the model (and validation rules):

namespace App\Livewire\Invoices;

use Livewire\Component;

class InvoiceCustomerDetails extends Component
{
    public $invoice;

    //Validation rules.
    protected $rules = [
        'invoice.customer_ref' => 'nullable|min:1|max:100',
        'invoice.date' => 'required|date_format:Y-m-d\TH:i:s', //'Date' field sends this format.
    ];

    public function render()
    {
        return view('livewire.invoices.invoice-customer-details');
    }
}

Then finally in the view you could wire:model to any of the attributes (provided you had declared a validation rule):

<div>

  <form wire:submit="submitForm" autocomplete="off">

    <div class="row">
      <div class="col-md-12 mt-1">
                
        <div class="row mb-2">
          <label for="CustomerRef" class="col-sm-4 col-form-label col-form-label-sm">Customer Ref</label>
          <div class="col-sm-8">
            <input wire:model.live.debounce.500ms="invoice.customer_ref" type="text" name="invoice.customer_ref" class="form-control form-control-sm @error('invoice.customer_ref') is-invalid @enderror" id="CustomerRef" placeholder="Customer reference" autofocus>
            @error('invoice.customer_ref')
              <div class="invalid-feedback">
                {{ $message }}
              </div>
            @enderror
          </div>
        </div>

        <div class="row mb-2">
          <label for="Date" class="col-sm-4 col-form-label col-form-label-sm">Date</label>
          <div class="col-sm-8">
            <input wire:model.live.debounce.500ms="invoice.date" type="datetime-local" name="invoice.date" class="form-control form-control-sm @error('invoice.date') is-invalid @enderror" id="Date" placeholder="dd/mm/yyyy H:i" @cannot('administer') disabled @endcannot>
            @error('invoice.date')
              <div class="invalid-feedback">
                {{ $message }}
              </div>
            @enderror
          </div>
        </div>


        <button type="submit" class="btn btn-sm btn-primary text-white float-end"><i class="fas fa-save me-1"></i> Save</button>

      </div>
    </div>

  </form>

</div>

Suffice to say, I can't get this working in Livewire 3 and I cannot find any documentation about it. It all starts working if I declare each attribute, and then add each attribute to the mouth method (or use the new fill function to mount them all).

Anyone having the same issue or able to advise on why they isn't working for me in Livewire3?

Thanks, Steve