You're not grabbing a valid blockhash:

tx.recentBlockhash = Keypair.generate().publicKey.toString();

Try replacing it with a recent blockhashh:

let latestBlockhash = await connection.getLatestBlockhash('finalized');
tx.recentBlockhash = latestBlockhash.blockhash;

You're not grabbing a valid blockhash:

tx.recentBlockhash = Keypair.generate().publicKey.toString();

Try replacing it with a recent blockhash:

let latestBlockhash = await connection.getLatestBlockhash('finalized');
tx.recentBlockhash = latestBlockhash.blockhash;