not a scam report

hello this is a small transaction that occurred, i would like to know who's fault for future reference too.

profile link: @StopReadingMyName
Amount: $15
Discord ID + Unique Discord ID: !James#0001 128297853285171200
Proof that it's their Discord:
Explanation of the trade: wanted to send LTC for a transaction, he put the first address and then after 3 minutes he said, oh wait and then put the 2nd address saying " i think this ltc 1"
my manager thought hes saying the first address by saying "ltc 1 "
How they scammed: claiming to not recieve transaction after putting the address, he claims he generated the address from his coinbase as well Screenshot - 65daf09d6d4c593cf2f345f306a7ec3c - Gyazo
Other relevant trade screenshots:
im willing to refund if need be, its just $15 but i wanna know who's really at fault in this case,
the reason it was sent after 10 minutes is because my manager was changing from usdt > ltc and then sending, and as u know binance ask for email + phone verification so things can take time.
he said he read "i believe its the ltc 1" and he thought hes referring first address, but customer claims that he generated first one from his coinbase

 

update: my manager decided to refund him, but i still would like to know who was at fault if possible, thanks.