This story is hard to follow because it got renamed after Blackmailed 2. It was originally called Blackmailed but got rereleased as Friendly Trade and parts 2-4 have the sub title Payback 1-3 just to keep things confusing.

The correct reading order is

Blackmailed 1/Friendly Trade 1
https://e-hentai.org/g/785128/680253ee5d/

Blackmailed 2/Friendly Trade 2 - Payback 1
https://e-hentai.org/g/785471/84b8c44fdd/ (This Comic)

Friendly Trade 2 - Payback 2-3
https://e-hentai.org/g/785993/5e030ab8b5/

After Friendly Trade finished two more stories come out that directly follow this story line. In order they are

Harsh Judgement 1-3
https://e-hentai.org/g/1040162/ba9583625b/

Community Service 1-3
https://e-hentai.org/g/972211/4839675ee0/

Base +6