Alright, so the 'Chased by My Possessive Ex' series is actually part of a pretty sprawling universe, and I've seen a few people get tripped up on the order. It started with 'Chased by My Possessive Ex' on GoodNovel or similar apps, which is the main story. After that, you've got 'My Ex's Possessive CEO Daddy' and 'The CEO's Little Mafia Queen.' The confusion usually comes from a prequel novella, 'Before He Was My Possessive Ex,' which was released later but chronologically happens before the main book.
I'd suggest reading the main novel first. The prequel assumes you already know the characters and their eventual toxic dynamic, so it hits harder if you've seen where they end up. Jumping into 'Before He Was...' first might spoil some of the central mystery about why the ex is so unhinged. Honestly, the reading order isn't as strict as some epic fantasy series, but following release order keeps the emotional payoffs intact. The later spin-offs with the CEO and mafia elements are fun, but they're more like standalone stories set in the same 'universe' of obsessive, high-stakes romance. You can pick those up anytime after the core book.
If you're reading on an app, just check the publication dates on the chapters; they're usually listed, and that's your safest guide. I tried reading the prequel first on a friend's recommendation and spent the whole time wondering when the famous 'chase' was gonna start, which was kinda my own fault.