Create Flow API returning repeated 502/504 errors since 23 September; other endpoints work

Hi Roman,

Would you mind sharing your request body (with any keys/PII/etc. redacted)? I’ve never used this endpoint before, I will give it a shot on my side and see what it returns.

Let me know.

Kevin.

​@roman loiale, I quickly checked on my end and am getting 201s (using 2026-04-15), so I’m not experiencing the same problem on my end.  

It’s possible there’s something large or complicated about your flow that’s leading to the timeout. In any case it’d be good to get someone from the Klaviyo team to take a look, cc ​@GabbyEsposito 


Cadence / Book a demo

Here’s the request body, redacted. It is a clone of a flow we already have live, with some minor changes. It is not a simple flow, but it is not our most complex one either. More importantly, it is almost exactly the same as a flow that’s already live.

https://gist.github.com/roman-loiale/4a365134f4e34688cf9c1ca954729446

Oh boy, that’s a big flow 😁

My assumption is that Klaviyo is timing out when trying to create the flow so it’s unable to return a response in time before Cloudflare’s logic kicks in and “closes the socket” (because the HTTP call was open for too long).

What happens if you try to create the first 25%, 50%, 75% of your flow? Are smaller flows timing out too? Are you able to test and determine a relationship between the size of the payload/flow and the 502/504s?

All the best,

Kevin.

Hi Roman, 

Meghan F. here from the Klaviyo Community team! This looks like a question our Support team would be able to look at in further detail. I am going to send a DM here to gather more details from you and open a ticket with the team accordingly!