Certainly! The Purchase-to-Pay process we'll model here involves several steps typically found in such a business process. This example will cover a simplified version of the process with the following steps:

1. **Create Purchase Order (PO)**: The initial step where a purchase order is created.
2. **Approve Purchase Order**: The purchase order needs approval before proceeding.
3. **Send Purchase Order to Supplier**: Once approved, the purchase order is sent to the supplier.
4. **Receive Goods**: Goods or services from the supplier are received.
5. **Receive Invoice from Supplier**: An invoice is received from the supplier after or along with the goods.
6. **Approve Invoice**: The received invoice is checked and approved.
7. **Process Payment**: Finally, payment is made to the supplier.

The steps **"Receive Goods"** and **"Receive Invoice from Supplier"** can often happen in parallel and not necessarily in a strict order. This aspect can be modeled as a choice in the POWL model if we assume they can't happen in parallel or as concurrent activities if we represent their possible parallel execution.

Here's a Python code using `pm4py` for this Purchase-to-Pay process where we model **"Receive Goods"** and **"Receive Invoice from Supplier"** as separate paths that can be executed in parallel to showcase the use of a partial order to handle parallelism:

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

# Defining the activities involved in the process
create_po = Transition(label="Create Purchase Order")
approve_po = Transition(label="Approve Purchase Order")
send_po = Transition(label="Send Purchase Order to Supplier")
receive_goods = Transition(label="Receive Goods")
receive_invoice = Transition(label="Receive Invoice from Supplier")
approve_invoice = Transition(label="Approve Invoice")
process_payment = Transition(label="Process Payment")

# As 'Receive Goods' and 'Receive Invoice from Supplier' can happen in parallel, we add them to a strict partial order
parallel_activities = StrictPartialOrder(nodes=[receive_goods, receive_invoice])

# Defining the sequence of activities
root = StrictPartialOrder(nodes=[create_po, approve_po, send_po, parallel_activities, approve_invoice, process_payment])

# Adding edges to define the flow
root.order.add_edge(create_po, approve_po)
root.order.add_edge(approve_po, send_po)
root.order.add_edge(send_po, parallel_activities)
root.order.add_edge(receive_goods, approve_invoice)
root.order.add_edge(receive_invoice, approve_invoice)
root.order.add_edge(approve_invoice, process_payment)

# This completes the setup for a simplified Purchase-to-Pay POWL model in pm4py
```

This code fragment demonstrates how to structure a basic Purchase-to-Pay process with parallel tasks using the POWL model in `pm4py`. For more complex processes, additional details and control flow constructs might be necessary.