Troubleshooting Metamask Internal JSON-RPC Errors on Polygon

Public RPCs can sometimes be slow, which could lead to such errors. There are alternative RPC options available on chainlist.

The issue may be related to the RPC URL used. Trying a different RPC might help resolve the problem.

It could be a network or RPC-related issue, as sometimes transactions succeed and other times they fail.

One of the most frequent reasons for encountering this error is improperly adding the Polygon network to MetaMask. If the RPC details (like the URL) are incorrect, it can lead to communication failures between MetaMask and the blockchain. But also it could be:

• Insufficient Gas Fees: Transactions on the Polygon network require native tokens (MATIC) to cover gas fees. If your wallet does not have enough tokens, transactions will fail, resulting in an internal JSON-RPC error.
• Outdated MetaMask Version: Using an outdated version of MetaMask can lead to compatibility issues and bugs that trigger this error. Regular updates are essential to ensure smooth operation.
• Hardware Wallet Issues: If you are using a hardware wallet (like Ledger), ensure that it is properly connected to MetaMask. Any connection issues can prevent successful transactions and lead to errors.
• Network Congestion or Bugs: Sometimes, issues may stem from network congestion or specific bugs within the Polygon network itself. For instance, there have been reports of bugs affecting deployed addresses on the Mumbai testnet, which could also impact mainnet interactions.

To resolve internal JSON-RPC errors, consider the following steps:

• Verify Network Settings: Double-check that you have added the Polygon network correctly in MetaMask, including accurate RPC URLs and chain IDs. Use official documentation or tools like Chainlist for guidance.
• Check Gas Fees: Ensure you have enough MATIC in your wallet to cover gas fees for transactions. You can transfer additional tokens if needed.
• Update MetaMask: Make sure you are using the latest version of MetaMask by checking for updates in your browser extension or app store.
• Reconnect Hardware Wallet: If applicable, disconnect and reconnect your hardware wallet to ensure it is properly linked to your MetaMask account.
• Test Different RPC Providers: If errors persist, try switching to a different RPC provider for Polygon. Some users have found success by using alternative nodes instead of the default ones provided by MetaMask.

Troubleshooting Metamask Internal JSON-RPC Errors on Polygon: Common Causes and Fixes

If you're working with a smart contract on Polygon and come across the dreaded "transaction failed: Internal JSON-RPC error" in Metamask, you're not alone. This is a common hurdle faced by Web3 developers, and while the error message itself is generic, it often points to specific, solvable problems:

1. Gas Limit Issues

Gas-related errors are among the most frequent reasons for transaction failures on Polygon. If the gas limit is too low, the transaction might fail mid-execution. Metamask typically estimates the gas limit automatically, but for certain smart contract interactions, manual adjustments are necessary.

Solution:
Manually increase the gas limit when submitting transactions. Here's how you can specify a higher gas limit programmatically in your code:

const tx = {
  to: contractAddress,
  data: contract.methods.someFunction().encodeABI(),
  gas: 500000, // Set a higher gas limit
};

web3.eth.sendTransaction(tx)
  .on('receipt', console.log)
  .on('error', console.error);

You can also monitor the current gas prices on Polygon using tools like Polygonscan Gas Tracker.

2. Smart Contract Errors

Errors in the smart contract itself can cause transactions to fail. For example, insufficient token allowances, unmet conditions in the code, or logic errors in your contract could trigger this issue.

Solution:

• Verify your smart contract code thoroughly.
• Ensure you’ve approved enough tokens for transfers, if applicable. For example:

// Approving tokens before interacting with the contract
const tx = await tokenContract.methods
  .approve(spenderAddress, web3.utils.toWei('100', 'ether'))
  .send({ from: userAddress });
console.log('Approval transaction hash:', tx.transactionHash);

Test Locally: Use tools like Hardhat or Ganache to simulate interactions with your contract in a local blockchain environment.

3. RPC Endpoint Limitations

Polygon’s public RPC endpoints can experience congestion, especially during periods of high traffic. This might result in timeouts or incomplete requests, causing JSON-RPC errors.

Solution:
Switch to a more reliable RPC provider like Alchemy, Infura, or QuickNode. Update your Metamask network configuration with an alternative RPC URL. Here’s an example of how to set up a connection programmatically:

const web3 = new Web3(new Web3.providers.HttpProvider('https://polygon-mainnet.g.alchemy.com/v2/YOUR_API_KEY'));

Custom Network Settings for Metamask:

• RPC URL: https://polygon-rpc.com/
• Chain ID: 137
• Symbol: MATIC

4. Insufficient MATIC for Fees

Even if your contract involves tokens other than MATIC, the Polygon network requires MATIC to cover gas fees. A wallet with insufficient MATIC will trigger transaction failures.

Solution:
Ensure your wallet has enough MATIC for gas fees. Check the current gas fee requirements and transfer additional MATIC if necessary:

const balance = await web3.eth.getBalance(userAddress);
console.log('MATIC Balance:', web3.utils.fromWei(balance, 'ether'));

5. Nonce Mismatch or Pending Transactions

Metamask uses a transaction nonce to keep track of the order of transactions. If there are pending transactions, subsequent ones may fail due to nonce mismatches.

Solution:
Reset your nonce to resolve this issue. In Metamask:

1. Go to Settings > Advanced > Toggle "Reset Account."
2. Resubmit your transaction with a manually updated nonce, like this:

const tx = {
  nonce: 10, // Replace with the correct nonce
  to: contractAddress,
  gas: 200000,
  data: contract.methods.someFunction().encodeABI(),
};

web3.eth.sendTransaction(tx)
  .on('receipt', console.log)
  .on('error', console.error);

6. Smart Contract Compatibility

If your contract was deployed with an outdated Solidity version, it might not fully align with the current EVM standards on Polygon.

Solution:
Verify the Solidity version used during deployment and update it if necessary. Recompile and redeploy the contract if compatibility issues arise.

Example: Upgrading Solidity Version

// Old Solidity version
pragma solidity ^0.5.0;

// Updated Solidity version
pragma solidity ^0.8.0;

7. Debugging with Polygonscan

When transactions fail, Polygonscan often provides detailed error logs. Copy the transaction hash from Metamask and search for it on Polygonscan to identify the exact error message.