The GitHub file doesn't have an introduction to how to install the file or some necessary questions so I dug a little bit into the code:
self.sender_key_label = tk.Label(self.frame, text="Enter Sender Private Key (Limit to 64 Alphanumeric)", font=("Arial", 9), bg='#8fbc8f')
self.sender_key_label.pack()
self.input_sender_key = tk.Entry(self.frame, validate="key", textvariable=self.sender_key_var, width=85, font=("Arial", 9), borderwidth=2, relief="raised", show="*")
self.input_sender_key['validatecommand'] = (self.input_sender_key.register(self.val_k),'%P','%d')
self.input_sender_key.pack()
Why does the Bitcoin payment services processor need to get the private key? This can be done by usiing the MPK and creating the wallet without risking exposing the private key.