At six weeks, I’d stop treating it like a casual reminder and move to a clear written follow-up.
Something like:
“Hi [Name], following up on the $1,200 invoice for the patio work completed on [date]. Payment is still outstanding. Could you confirm when payment will be made? If there’s an issue with the work or invoice, please let me know today so we can resolve it.”
Still professional, but more explicit. The important part is having the amount, work performed, invoice status, and requested action in writing.