Flagsmith key type must match the evaluation mode

TL;DR

Keep server-side tokens out of client bundles.

Steps

1. Pair the key to the mode: server-side token for local evaluation, environment key for remote. Keep server-side tokens out of client bundles. After changing a flag in the dashboard, wait out the 60-second refresh or trigger a manual refresh before concluding the SDK is broken.

When to use

You are seeing this: Pair the key to the mode: server-side token for local evaluation, environment key for remote. Use this skill when you run into "Flagsmith key type must match the evaluation mode".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Source: Official docs (Flagsmith server-side SDKs): the API token you configure is either the Environment API key or the Server Side SDK Token, depending on whether you run local or remote evaluation. Mixing them up is a common auth failure: a client-side environment key cannot drive local evaluation, and a server-side token in browser code leaks a credential that can read every flag in the environment. The SDK overview adds that local mode makes no further network calls for 60 seconds after init, so flag edits are invisible until the next refresh.

Verified resolution: Pair the key to the mode: server-side token for local evaluation, environment key for remote. Keep server-side tokens out of client bundles. After changing a flag in the dashboard, wait out the 60-second refresh or trigger a manual refresh before concluding the SDK is broken.

Source URL: https://docs.flagsmith.com/integrating-with-flagsmith/sdks/