Do I need to send the original Receipt of Notification when filing a 90-day report by post in Thailand?

I’m finally giving up on doing the 90-day report online. it’s just way too hit and miss and in fact more miss than hit these days! Does anyone know, when you do it by Thai post, whether you need to send the original Receipt of Notification (with the red writing) in the envelope, or can a photocopy do? I’m worried about sending the only proof I have of doing the last 90-day report which I had to do in person due to what I said about the hit and miss stuff above. TIA.