The situation:
Using the kagiapi Python package from main against the Kagi Search API, every request passed with cache=True consistently returned a 500 Internal Server Error. The other search parameters worked, so the reporter suspected the cache flag handling specifically.
What actually fixes it (verified in the thread):
The bug was in how the package serialized the flag: it sent the GET parameter capitalized as True/False, which the Kagi API rejects with a 500. PR #5 (merged the same day) fixed it by lowercasing the cache parameter so it goes out as true/false. Workaround if you are on an older checkout: pass the cache value as a lowercase string yourself, or upgrade to a version containing PR #5.