Here's an example implementation of a POWL model for a basic Purchase-to-Pay process in pm4py:
```python
import pm4py
from pm4py.objects.powl.obj import StrictPartialOrder, OperatorPOWL, Transition, SilentTransition
from pm4py.objects.process_tree.obj import Operator

# Define the activity nodes
proc_order = pm4py.objects.powl.obj.StrictPartialOrder(
    nodes=[
        proc_orderMui = OperatorPOWL(
            operator=Operator.XOR,
            children=[
                proc_orderMuiProcurement = Transition("Procurement"),
                proc_orderMuiRequisition = Transition("Requisition")
            ]
        ),
        proc_order Commit = OperatorPOWL(
            operator=Operator.LOOP,
            children=[
                proc_orderCommitInvoice = Transition("Invoice"),
                proc_orderCommitInvoiceSilent = SilentTransition()
            ]
        ),
        proc_order Authorization = Transition("Authorization"),
        proc_orderPreparation = Transition("Preparation"),
        proc_orderConfirmation = Transition("Confirmation"),
        proc_orderPayment = Transition("Payment")
    ]
)

# Define the control flow graph
proc_order.order.add_edge(proc_orderMui, proc_orderMui_procurement)
proc_order.order.add_edge(proc_orderMui, proc_orderMuiRequisition)

proc_order.order.add_edge(proc_orderMuiProcurement, proc_orderCommit)
proc_order.order.add_edge(proc_orderMuiRequisition, proc_orderCommit)

proc_order.order.add_edge(proc_orderCommit, proc_orderAuthorization)
proc_order.order.add_edge(proc_orderCommitInvoice, proc_orderAuthorization)
proc_order.order.add_edge(proc_orderCommitInvoiceSilent, proc_orderAuthorization)

proc_order.order.add_edge(proc_orderAuthorization, proc_orderPreparation)
proc_order.order.add_edge(proc_orderConfirmation, proc_orderPreparation)

proc_order.order.add_edge(proc_orderPreparation, proc_orderPayment)
proc_order.order.add_edge(proc_orderConfirmation, proc_orderPayment)

proc_order.order.add_edge(proc_orderPayment, proc_orderConfirmation)

# Print the control flow graph (optional)
print(proc_order.order.edges())
```
This code defines a POWL model for a basic Purchase-to-Pay process with the following steps:

* Procurement
* Requisition
* Commit
	+ Invoice and silent transition (i.e., a payment without invoices)
		- loops until committed
* Authorization
* Preparation
* Confirmation
* Payment

Note that this implementation is a basic example to illustrate how to create a POWL model in pm4py. In practice, the model will likely be more complex