Sepolia Testnet

An API key generated on Etherscan ​ can be used across all mainnet and testnet explorers.

Similarly, all endpoints and parameter formatting remain the same across testnet explorers, you are only required to change the relevant API endpoint URL as follows.

Network	URL	Documentation
Mainnet	https://api.etherscan.io/api	https://docs.etherscan.io/
Goerli	https://api-goerli.etherscan.io/api	https://docs.etherscan.io/v/goerli-etherscan
Sepolia	https://api-sepolia.etherscan.io/api	https://docs.etherscan.io/v/sepolia-etherscan/

Source attribution via a backlink or a mention that your app is "Powered by Etherscan APIs" is required except for personal/private usage.