Polygon RPC Error Fixes for Internal JSON-RPC and Connection Issues

05 September 2026

You are trying to send a transaction on Polygon. MetaMask spins. Then you see it: "Internal JSON-RPC error." Or maybe "connection not open." The transaction never goes through. This is one of the most common problems on Polygon. It is also one of the easiest to fix.

What the JSON-RPC error actually means

Polygon, like every blockchain, needs an endpoint to talk to your wallet. That endpoint is called an RPC (Remote Procedure Call) URL. When you add Polygon to MetaMask, the wallet uses a public RPC by default. Public RPCs are free. They are also shared by thousands of other users.

The error means your request never reached the chain, or it reached the chain but the response got lost. Either way, the connection between your wallet and the network is broken. The RPC provider is overwhelmed, rate-limited, or temporarily down.

Public RPC endpoints have hard limits. Polygon's official public RPC can handle only so many requests per second. When traffic spikes, it drops connections. That is when you see the JSON-RPC error. It is not your fault. It is not your transaction's fault. It is the endpoint's fault.

The fix: switch to a private or alternative RPC

The solution is straightforward: stop using the default public RPC and replace it with a different endpoint.

Private RPC services like Alchemy and Infura give you a dedicated URL. You sign up for a free account, they give you an API key, and you paste that key into your wallet's network settings. That single change eliminates most JSON-RPC errors.

Here is how to do it in MetaMask. Open Settings. Go to Networks. Find Polygon Mainnet. Click it. You will see the RPC URL field. Delete the old one. Paste your new one. Save.

The same fix works on WalletConnect, Trust Wallet, and any other wallet that lets you edit network details. If your wallet does not let you edit RPCs, you need a different wallet.

Where to find working RPC URLs

Alchemy and Infura are the two most reliable providers. Both offer free tiers, both have Polygon endpoints, and both are used by major dApps and exchanges.

Alchemy's Polygon endpoint looks like this: https://polygon-mainnet.g.alchemy.com/v2/YOUR_API_KEY. Infura's looks like: https://polygon-mainnet.infura.io/v3/YOUR_API_KEY. You get the key after signing up. The process takes two minutes.

There are other options: QuickNode, Chainstack, and public endpoints from Polygon's documentation. But Alchemy and Infura are the safest bets. They have the most uptime and the clearest documentation.

You can also try a different public RPC. Polygon maintains a list of public endpoints on their official documentation. Some work better than others. Try one. If it fails, try the next. This is a temporary fix. Public endpoints will always be unreliable during congestion.

When the error is not the endpoint

Not every JSON-RPC error is an RPC problem. Sometimes the error is about your transaction itself.

If you see "gas required exceeds allowance" or "intrinsic gas too low," the issue is your gas settings. Polygon transactions need gas. If you set gas too low, the network rejects the transaction. The error message looks like an RPC error but is actually a gas error. Check your gas limit. Increase it. Try again.

If you see "nonce too low" or "replacement transaction underpriced," the issue is transaction ordering. You have a pending transaction stuck in the mempool. You need to clear it, speed it up, or cancel it. MetaMask has a built-in option for this. Click the pending transaction. Choose Speed Up or Cancel.

If you see "insufficient funds," you do not have enough MATIC. Polygon needs MATIC for gas, not the token you are trying to send. Check your balance. Add MATIC if needed.

A quick checklist

When you get a JSON-RPC error on Polygon:

1. Try the transaction again in 30 seconds. Sometimes the endpoint recovers.
2. Switch to a private RPC from Alchemy or Infura.
3. Check your gas limit. Make sure it is not too low.
4. Check for stuck pending transactions. Clear them.
5. Verify your MATIC balance covers gas.
6. Restart your wallet. Sometimes a clean session fixes connectivity.

What this page does not cover

This page is about RPC errors specifically. It does not cover bridge issues, token visibility, or wallet security. Those are separate problems with separate fixes. Other pages on this site cover them in detail.

The bottom line

JSON-RPC errors on Polygon are almost always endpoint congestion. Public RPCs are free but unreliable. Switch to a private RPC. That fixes the problem in most cases. If it does not, the error is probably about gas or a stuck transaction. Diagnose from there.

The fix takes two minutes. The error is frustrating but trivial. You do not need to understand blockchain architecture. You just need a different URL.

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