In 2023, Fullstory made improvements to our capture process to improve both overall availability and the delay before which capture begins. A by-product of these changes is that the output of the getSession API (applies both to V1 API FS.getCurrentSessionURL() and V2 API FS('getSession')) will also change. Specifically, URLs output by the getSession API will no longer include /session/ and will instead read /client-session/.
If you have built a custom integration which is reliant on that specific URL structure (e.g. <userid:session> information is parsed out after /session/), then this change will result in an error in your integration. You may also encounter issues related to the session replay URL returned in webhook payloads being different than the URL returned by the browser API, or related to the length of the URL changing. It's important to know that Fullstory will only consider the full URL part of the contract, therefore any parsing of the URL components should be done at your own risk.
Read more here: Breaking Changes