Sure! Here is an example of how you can implement a POWL model for a Purchase-to-Pay process using pm4py:

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

# Define transitions for each step in the Purchase-to-Pay process
request_goods = Transition(label="Request Goods")
approve_purchase = Transition(label="Approve Purchase")
order_goods = Transition(label="Order Goods")
receive_goods = Transition(label="Receive Goods")
pay_supplier = Transition(label="Pay Supplier")

# Define the partial order between the steps in the Purchase-to-Pay process
root = StrictPartialOrder(nodes=[request_goods, approve_purchase, order_goods, receive_goods, pay_supplier])
root.order.add_edge(request_goods, approve_purchase)
root.order.add_edge(approve_purchase, order_goods)
root.order.add_edge(order_goods, receive_goods)
root.order.add_edge(receive_goods, pay_supplier)

# Generate a POWL model for the Purchase-to-Pay process
pm4py.objects.powl.obj.applyModel(root)
```

This code defines the transitions for each step in the Purchase-to-Pay process (e.g., requesting goods, approving purchase, etc.) and establishes the partial order between these steps. Finally, it generates a POWL model for the Purchase-to-Pay process using pm4py.

Please note that this is just a simplified example and you may need to adjust the transitions and partial order based on your specific Purchase-to-Pay process requirements.