WHO: Ventress at Derpibooru and ych.commishes.com, VentressTheBat at Discord, ffighterbrent at DeviantArt, ventressthebat at FurAffinity.
WHERE: the commission was received via ych.commishes.com, with further communications in Discord.
WHAT: a digital art piece ($475). Here is the auction page: https://ych.commishes.com/auction/show/1BTR/come-get-some/ (NSFW), here is the finished piece: https://ych.commishes.com/followUp/show/1BTR/come-get-some/ (NSFW). It was a collaborative YCH by me and another artist (Yakovlev-Vad), but I've handled all communications and payments, so there will be no proxy writing — this detail will just make the logs easier to understand.
December 8, 2017: commission accepted, payment schedule agreed upon (first payment on December 14, Thursday, and then every Thursday after that, 4 parts, 125+125+125+100 USD).
December 15, 2017: the final picture delivered to the commissioner, I receive the first part of the payment ($125).
December 29, 2017: I receive the second installment ($125).
January 13, 2018: I remind the commissioner about the payment due and eventually get banned from their Discord and DA. Also, I send them a Paypal invoice for $225 that isn't paid to this day.
On December 5, 2017, I've launched a Christmas-themed YCH auction (https://ych.commishes.com/auction/show/1BTR/come-get-some/, NSFW). On December 8 it was won by Ventress. I've done several commissions for Ventress before and knew them as a reliable and responsible customer, so when they asked for paying in several installments, I was happy to oblige.
I've delivered the finished piece (https://ych.commishes.com/followUp/show/1BTR/come-get-some/, NSFW) on December 15th with no further requests or complaints from the customer. Also, this day I've received the first part of the payment and we've agreed to shift the payment schedule one day forward (so it would have been Dec 15 - Dec 22 - Dec 29 - Jan 5).
I've reminded the commissioner about the payment due on December 23th. They said that they needed more time (https://i.imgur.com/hiwoXpU.png). I've received this second part on December 29th.
I didn't want to spoil the holidays for Ventress with monetary issues, so I've sent my second reminder on January 13th (according to our agreement, the commission should have been paid in full by this time). After a short dialogue (https://i.imgur.com/ybbMowr.png, mild language) I got banned from their Discord. I've also sent the commissioner a Paypal invoice for the remaining amount ($225) on January 13th and a Paypal reminder about it on February 2nd, but this invoice isn't paid to this day.
Here are the Discord logs and a relevant part of my Paypal record:
UPDATE (Mar 04): I've received the rest of the payment (proof: https://orig00.deviantart.net/d553/f/2018/062/f/0/upd_by_tomatocoup-dc4uxws.jpg).