To create a POWL model for a hypothetical Purchase-to-Pay process using the `pm4py` library, we first need to understand the typical steps involved in such a process. Common stages in a Purchase-to-Pay process include requisitioning, approval, purchase order creation, receipt of goods/services, invoice receipt, and payment processing. Based on this understanding, we'll define a workflow in the partially ordered workflow language (POWL).

Let's construct the Python code using these steps:

1. **Requisition** (`Requisition`): Initiating a purchase by requesting goods or services.
2. **Approval** (`Approval`): The requisition is approved.
3. **Create Order** (`CreateOrder`): A purchase order is created post-approval.
4. **Receive Goods** (`ReceiveGoods`): Goods or services ordered are received.
5. **Invoice Received** (`InvoiceReceived`): An invoice is received following the receipt of goods.
6. **Payment Process** (`PaymentProcess`): Payment is processed post-invoice receipt.

In the real-world scenario, the process from approval to creating a purchase order might involve choice (e.g., manual or automatic order), and after receiving an invoice, there might typically be a verification loop where the invoice is verified against the order and goods received before proceeding to payment.

Here's how the code could look using `pm4py`:

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

# Defining transitions
Requisition = Transition(label="Requisition")
Approval = Transition(label="Approval")
CreateOrder = Transition(label="CreateOrder")
ReceiveGoods = Transition(label="ReceiveGoods")
InvoiceReceived = Transition(label="InvoiceReceived")
PaymentProcess = Transition(label="PaymentProcess")

# Defining a choice for order creation method (Manual or Automatic)
ManualOrder = Transition(label="ManualOrder")
AutomaticOrder = Transition(label="AutomaticOrder")
orderChoice = OperatorPOWL(operator=Operator.XOR, children=[ManualOrder, AutomaticOrder])

# Defining a loop for invoice verification (the process might need to revisit invoice verification conditionally)
InvoiceVerification = Transition(label="InvoiceVerification")
verifyLoop = OperatorPOWL(operator=Operator.LOOP, children=[InvoiceReceived, InvoiceVerification])

# Defining the main model with partial order
PurchaseToPay = StrictPartialJar(nodes=[Requisition, Approval, orderChoice, ReceiveGoods, verifyLoop, PaymentProcess])
PurchaseToPay.order.add_edge(Requisition, Approval)
PurchaseToPay.order.add_edge(Approval, orderChoice)
PurchaseToPay.order.add_edge(orderChoice, ReceiveGoods)
PurchaseToPay.order.add_edge(ReceiveGoods, verifyLoop)
PurchaseToPay.order.add_edge(verifyLoop, PaymentProcess)

# The constructed model defines a typical Purchase-to-Pay process with choices and loops modeled explicitly
```

This model allows processing an order either manually or automatically post-approval, and it involves a verification loop for the invoice before proceeding to make a payment. Each step is clearly laid out with choices and loops modeled to reflect possible real-life business logics. Adjust this template based on the specific rules and conditions of your Purchase-to-Pay process.