Hello @Eugene K,

Thanks for sharing this question with the Klaviyo Community!

As stated within the Klaviyo API Documentation under Rate Limits:

All of these endpoints are rate limited. You should be sure to check the response codes and retry requests that exceed the rate limit at a later time. If you hit rate limits, we recommend adjusting your request-rate using an exponential backoff

Each of the Klaviyo endpoints have a varied rate limit. The backoff value should be returned in the response from the API request you are making to these endpoints to allow you to adjust them to avoid being limited. 

If you were interested in connecting your own custom integration with Klaviyo, I would recommend taking a look at the below articles Klaviyo offers on this topic:

• Getting Started with Klaviyo APIs
• Track and Identify API Reference
• Klaviyo's REST API References
• Setting Up API-based Transactional Events
• Setting Up API-based Website Activity Events
• Integrate a Standard Ecommerce Platform
• Integrate a Subscription Ecommerce Platform
• Technical Terms Glossary

If you need hands on assistance in building out your custom integration, you can also reach out to extensive network Klaviyo Partners for further guidance. More details on this process and the benefits of pursuing a Klaviyo partner can be found in the post below:

https://community.klaviyo.com/job-board-55/tips-for-hiring-a-klaviyo-partner-770

-David