Sure, here is a simple implementation of a Partial Order Workflow Language (POWL) model based on the concept that a `Purchase-to-Pay` process typically involves ordering items, approving orders, and then making payments. 

This code snippet assumes there are three major steps in this hypothetical workflow:

1. **Ordering Items**: This could include activities such as selecting items from a catalog or creating an order.
2. **Approving Order**: This would be the approval of the created item order.
3. **Processing Payment**: Once approved, payment is processed for the ordered items.

Let's create this workflow using `pm4py` library in Python:

```python
import pm4py
from pm4py.objects.powl.obj import StrictPartialOrder, OperatorPOWL, Transition, SilentTransition

# Create nodes/activities (Transitions)
order_items = Transition(label="Order Items")
approve_order = Transition(label="Approve Order")
process_payment = Transition(label="Process Payment")

# Create silent transitions to model actions that don't need approval
complete_order = SilentTransition()
cancel_order = SilentTransition()

# Model for Approving Order: If approved, continue with processing payment; if denied, cancel order.
approve_or_cancel_model = OperatorPOWL(operator=Operator.XOR,
                                       children=[process_payment, cancel_order])

# Model for Ordering Items: This leads to both the approve model and a silent transition for completion.
order_items_model = StrictPartialOrder(nodes=[order_items, approve_or_cancel_model])
order_items_model.order.add_edge(order_items, approve_or_cancel_model)
order_items_model.order.add_edge(order_items, complete_order)

# Complete Purchase-to-Pay Workflow: Start with ordering items, then branch into approval and payment processes.
purchase_to_pay_process = StrictPartialOrder(nodes=[order_items_model])
```

This POWL model defines a workflow starting from `Order Items` as the main activity. Depending on whether this item order is approved (`Approve Order`), it leads to either processing payment (`Process Payment`) or cancellation of the order (through `Cancel Order`). Both paths are silent transitions, representing completion actions that do not involve explicit decision-making.

In your real implementation, you can adjust labels and child nodes as per your actual process requirements.