Signing and sending Memo transaction instead of signed message

signTx.ts

        const nonce = await getCsrfToken();
        if (!nonce) {
          throw new Error("Missing nonce.");
        }

        const tx = new Transaction();
        tx.add(
          new TransactionInstruction({
            programId: new PublicKey(
              "MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr"
            ),
            keys: [{ pubkey: publicKey, isSigner: true, isWritable: false }],
            data: Buffer.from(nonce, "utf8"),
          })
        );

        const blockHash = await connection.getLatestBlockhash("finalized");

        tx.feePayer = publicKey;
        tx.recentBlockhash = blockHash.blockhash;

        const signedTransaction = await signTransaction(tx);
        const signedTransactionSerialized = signedTransaction
          .serialize({ requireAllSignatures: false })
          .toString("hex");

        await signIn("credentials", {
          signedTransactionSerialized: signedTransactionSerialized,
          pubkey: bs58.encode(publicKey.toBytes()),
          redirect: true,
          callbackUrl: searchParams?.get("from") ?? "/dashboard",
        });
      } catch (error) {
        setError(error);
        console.error(error);
        toast({
          message: error.message || "Failed to sign transaction",
          type: "error",
        });
      }