If you send bitcoins to an invalid address on the blockchain, the funds will be lost forever. This is because each blockchain has its own unique way of recording and encoding addresses, so if you enter the wrong address, the transaction will not be recognized by the intended blockchain and will not be processed. For example, if you enter a Litecoin address as a Bitcoin transfer recipient, your wallet will tell you that the address is invalid because it is not compatible with the Bitcoin blockchain. Similarly, if you enter a nonexistent Bitcoin address or an address that you do not control (i.e. you do not have the corresponding private key), the funds will be irretrievably lost.
It is important to note that cryptocurrency transactions are irreversible, which means that once a transaction is confirmed on the blockchain, it cannot be canceled, altered, or reversed. This means that sending cryptocurrency to the wrong wallet address can result in permanent loss of funds. To avoid this, it is important to double-check the address you are sending to and use validation tools to ensure its validity. It is also a good idea to verify the address on a block explorer and avoid sending funds to addresses that appear to be valid but are not associated with the intended recipient.