The Casa App uses an HD (hierarchical deterministic) Bitcoin key, which generates a new address with each transaction that's made.
When sending bitcoin, leftover amounts in addresses get returned to the sending wallet in a new address. This is known as a "change" address.
Some hardware wallet devices, like a Trezor, may ask you to confirm an additional "change" address when sending funds from the Casa App.
For more information on how change addresses work, and why it's built into the Bitcoin protocol, see https://en.bitcoin.it/wiki/Change
What if I want to whitelist an address with an exchange?
Some Bitcoin exchanges offer the ability to whitelist a BTC withdrawal address for additional security (Swan, Kraken, Coinbase, Gemini, etc...).
It's fine to whitelist a Casa deposit address with the exchange, and make multiple withdrawals to the same address, even though Casa App may show you a different deposit address.
NOTE: As an exception to the above, please keep in mind that if you ever transfer funds to a new keyset in the Casa App in what we call a Key Rotation - which you may do if, for example, you want to replace a hardware wallet device in the future - you should not send to that address, since it would then be part of your old keyset.