An address is checksummed if it uses both upper- AND lowercase letters instead of just lowercase letters. Checksummed addresses are meant to help prevent users from sending transactions to the wrong address.

How to checksum an address:

The easiest option is to get a checksummed version of an Ethereum address is to open the address on etherscan.io and copy it from there.

e.g. https://etherscan.io/address/0x448E4E6DD37523A5c7804D75a67754c24bFbFb32/

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