I would wait 6 days then send. Hi this is a friendly reminder your payment is due.
Simple and sweet..
I totally agree but did this on day 5. Buyer did pay the next day but left me a neutral feedback yet said she liked the product. I wrote to her and asked her why the neutral, I was a little ticked. She said because of my reminder. Here's her response, I copied and pasted. Hope I don't get in trouble for doing that but did leave her name out. She basically called me greedy and impatient. Greedy mind you, the item sold for a lousy $12!.......here is the reply.
"Yes, and I'm sure you think that's the appropriate response, too - which of course, it is not.
One of the things that made eBay a wonderful place to shop when I first joined was the grace of time - which has been shortened and shortened due to greed & impatience.
But, jsyk, regardless of how few days a seller demands for payment, eBay automatically gives a buyer 7 days & then another 7 for the NP dispute to be lodged & paid, if that's how it has to go. But some sellers still have patience & just give grace automatically. God put those people - those with grace - here to help keep the species sane.
Also, if we buyers weren't meant to have 60 days for FB - it used to be 90, btw - we wouldn't have 60 days.
I almost always give positive FB, and a seller has to do something really annoying one way or another to get a neutral - and has to be plain godawful to get a negative from me.
If FB was all positive all the time it would be a worthless indicator."