> ## Documentation Index > Fetch the complete documentation index at: https://docs.kleap.co/llms.txt > Use this file to discover all available pages before exploring further. # Error Reference > Common error messages and how to fix them A guide to common error messages and their solutions. ## Build Errors ### Module not found ``` Error: Cannot find module '@/components/Button' ``` **Cause**: The imported file doesn't exist or path is wrong. **Fix**: ``` The import '@/components/Button' can't be found. Can you check if the file exists and fix the import path? ``` *** ### Unexpected token ``` SyntaxError: Unexpected token '<' ``` **Cause**: JavaScript syntax error, often in JSX. **Fix**: ``` Getting a syntax error "Unexpected token". Can you find and fix the syntax issue? ``` *** ### Type error ``` Type 'string' is not assignable to type 'number' ``` **Cause**: TypeScript type mismatch. **Fix**: ``` Getting this type error: [full error message] Can you fix the type issue? ``` *** ### Export not found ``` Attempted import error: 'Button' is not exported from './components' ``` **Cause**: Component exists but isn't exported. **Fix**: ``` The 'Button' component isn't exported properly. Can you add the export to the component file? ``` ## Runtime Errors ### Cannot read properties of undefined ``` TypeError: Cannot read properties of undefined (reading 'map') ``` **Cause**: Trying to use a method on undefined/null value. **Fix**: ``` Getting "Cannot read properties of undefined" when mapping over data. Can you add a check for undefined and handle the empty state? ``` *** ### X is not a function ``` TypeError: response.json is not a function ``` **Cause**: Variable isn't what you expect. **Fix**: ``` Getting "[x] is not a function" error. Can you check the variable type and fix the function call? ``` *** ### Network error ``` TypeError: Failed to fetch ``` **Cause**: API request failed (network, CORS, or server error). **Fix**: ``` API fetch is failing with a network error. Can you check the API endpoint and error handling? ``` ## React Island Errors These happen inside interactive React components (islands) on your Astro site. ### Hydration mismatch ``` Hydration failed because the initial UI does not match what was rendered on the server ``` **Cause**: The static HTML and the hydrated island render different content. **Fix**: ``` Getting a hydration mismatch error. Can you fix the component to render the same on server and client? ``` Common causes: * Using `Date.now()` or `Math.random()` directly * Accessing `window` or `localStorage` without checks * Conditional rendering based on browser-only values *** ### Invalid hook call ``` Invalid hook call. Hooks can only be called inside of the body of a function component ``` **Cause**: Hook used incorrectly. **Fix**: ``` Getting "Invalid hook call" error. Can you check that hooks are only used in function components and not inside conditions or loops? ``` *** ### Too many re-renders ``` Error: Too many re-renders. React limits the number of renders ``` **Cause**: Component is in infinite render loop. **Fix**: ``` Getting "Too many re-renders" error. Can you find and fix the infinite loop in the component? ``` Usually caused by: * Calling `setState` directly in render * Missing dependency array in `useEffect` * State update triggering another state update ## Database Errors ### Permission denied on a row ``` This action isn't allowed for the current user on table "posts" ``` **Cause**: Data is scoped per user, and this operation isn't permitted for the signed-in user. **Fix**: ``` Getting a permission error when [inserting/updating/deleting] data. Can you check that the data rules let the right users read and write this table? ``` *** ### Foreign key violation ``` insert or update on table "posts" violates foreign key constraint ``` **Cause**: Referenced record doesn't exist. **Fix**: ``` Getting foreign key violation error. The referenced [table] record doesn't exist. Can you fix the query or create the referenced record first? ``` *** ### Duplicate key ``` duplicate key value violates unique constraint ``` **Cause**: Trying to insert duplicate value in unique column. **Fix**: ``` Getting duplicate key error. Can you add a check for existing records or use upsert? ``` ## Authentication Errors ### Session not found ``` Auth session missing — no signed-in user ``` **Cause**: User not logged in or session expired. **Fix**: ``` Getting "session missing" error. Can you add authentication check and redirect to login if not authenticated? ``` *** ### Invalid login credentials ``` Invalid login credentials ``` **Cause**: Wrong email or password. **Fix**: This is expected for wrong credentials. Ensure your error handling shows a user-friendly message. ## Environment Variable Errors ### Missing environment variable ``` Error: Missing environment variable: PUBLIC_API_URL ``` **Cause**: Required variable not set. (In Astro, browser-exposed variables are prefixed with `PUBLIC_`.) **Fix**: 1. Go to Settings > Environment 2. Add the missing variable 3. Redeploy if in production ## Quick Reference Table | Error Contains | Likely Cause | Quick Fix | | --------------------- | ---------------------- | ------------------------ | | `Cannot find module` | Wrong import | Check file path | | `undefined` | Missing data | Add null check | | `not a function` | Wrong variable type | Check variable | | `Hydration` | Server/client mismatch | Fix SSR | | `Invalid hook` | Hook misuse | Check hook rules | | `Too many re-renders` | Infinite loop | Fix useEffect/setState | | `not allowed` | Per-user data rule | Check table access rules | | `Failed to fetch` | Network/API issue | Check endpoint | | `PUBLIC_` | Env var missing | Add to settings | ## Getting More Help If an error isn't listed here: 1. **Copy the full error message** 2. **Paste it to Kleap AI** with context about what you were doing 3. **Check browser console** for additional details Step-by-step solutions to common problems