Delete DHCP-Reservation via Python Script

I want to delete DHCP Reservations using a Python script and have the following code:

import tkinter as tk
from tkinter import messagebox
import subprocess

def delete_reservation():
    dhcp_server = "My DHCP-Server"
    scope = "Scope-IPAddress"
    ip_reservation = entry_ip.get().strip()

    if not ip_reservation:
        messagebox.showwarning("Error", "Please enter a IP-Address.")
        return

    try:
        ps_command = (
            f"Remove-DhcpServerv4Reservation "
            f"-ComputerName {dhcp_server} "
            f"-ScopeId {scope} "
            f"-IPAddress {ip_reservation} "
            f"-Confirm:$false"
        )

        subprocess.run(["powershell", "-Command", ps_command], check=True)
        messagebox.showinfo("Success", f"Reservation {ip_reservation} Has been deletes successfully")
    except subprocess.CalledProcessError as e:
        messagebox.showerror("Error", f"Couldn't delete reservation:\n{e}")

root = tk.Tk()
root.title("Delete DHCP-Reservation")
root.geometry("350x150")

tk.Label(root, text="IP-Address of Reservation:").pack(pady=10)
entry_ip = tk.Entry(root, width=30)
entry_ip.pack()

tk.Button(root, text="Delete", command=delete_reservation, bg="#d9534f", fg="white").pack(pady=20)

root.mainloop()

Somehow it wont execute. The error im getting is "... returned non-zero exit status 1."