Dear Lee,
Thank you for your invoice which I settled this morning.
I am very pleased with the excellent work you did for me last week and the careful clearing-up you did before leaving. You will be welcome here at any time.
If at any time you found yourself looking for work (it seems unlikely), I have one or two doors in need of help or replacement and I should be very pleased to welcome you here again.
With many thanks,
Yours sincerely,
Lawrence L.