Hello @ISSandboxes
As @ernst.stefan has said, the Agile functionality is provided by the Jira Cloud SOFTWARE module, which has separate REST APIs to the Jira Cloud platform itself.
Refer to this forum thread where this topic has been previously discussed, or search this forum for ‘sprint rest api’ for other times the same topic has been raised.
For more on the different between Jira and Jira Software, Google ‘jira vs jira software’