hardhat problem when testing

[mohamedtb20]

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C:\Users\DELL\nft_marketplace>npx hardhat test
Error HH8: There's one or more errors in your config file:

• Invalid account: #0 for network: mumbai - Expected string, received function
• Invalid account: #0 for network: mainnet - Expected string, received function

To learn more about Hardhat's configuration, please go to https://hardhat.org/config/``

[alcuadrado]

Please, take a look at the config values and double-check your config.