ethers.js/docs/v5/api-keys

Documentation: html

Provider API Keys

Etherscan

INFURA

Alchemy

Creating a Default Provider

// Use the mainnet
const network = "homestead";

// Specify your own API keys
// Each is optional, and if you omit it the default
// API key for that service will be used.
const provider = ethers.getDefaultProvider(network, {
    etherscan: YOUR_ETHERSCAN_API_KEY,
    infura: YOUR_INFURA_PROJECT_ID,
    alchemy: YOUR_ALCHEMY_API_KEY
});