How to Sign transaction from btc 1...(address) to taproot? I am an iOS developer.

[wcj233]

How to Sign transaction from btc 1...(address) to taproot?
eg: transer from 1F7Ewa83qDyCYqkVuDDarLXAfDvdAHpQvw to bc1ph8cj9jdtzkjgtmfw39zf52xyz3jds4hjp6088ljl59zus0d2wc4s4uhv3u.

I can sign transaction from btc 1...(address) to btc 3...(address), but to taproot, failed.

[satoshiotomakan]

Hi @wcj233, thank you for the question.
Please take a look at the BRC20 transaction example:

wallet-core/tests/chains/Bitcoin/TWBitcoinSigningTests.cpp

Lines 423 to 471 in 7cd532c

	// Tests the BitcoinV2 API through the legacy `SigningInput`.
	TEST(BitcoinSigning, SignBRC20TransferCommitV2) {
	auto privateKey = parse_hex("e253373989199da27c48680e3a3fc0f648d50f9a727ef17a7fe6a4dc3b159129");
	auto fullAmount = 26400;
	auto minerFee = 3000;
	auto brcInscribeAmount = 7000;
	auto forFeeAmount = fullAmount - brcInscribeAmount - minerFee;
	auto txId = parse_hex("089098890d2653567b9e8df2d1fbe5c3c8bf1910ca7184e301db0ad3b495c88e");
	PrivateKey key(privateKey);
	auto pubKey = key.getPublicKey(TWPublicKeyTypeSECP256k1);
	TW::BitcoinV2::Proto::SigningInput signing;
	signing.set_version(2);
	signing.set_private_key(key.bytes.data(), key.bytes.size());
	signing.set_input_selector(TW::Utxo::Proto::InputSelector::UseAll);
	signing.set_disable_change_output(true);
	auto& in = *signing.add_inputs();
	in.set_txid(txId.data(), txId.size());
	in.set_vout(1);
	in.set_value(fullAmount);
	in.mutable_builder()->set_p2wpkh(pubKey.bytes.data(), pubKey.bytes.size());
	auto& out = *signing.add_outputs();
	out.set_value(brcInscribeAmount);
	auto& brc20 = *out.mutable_builder()->mutable_brc20_inscribe();
	brc20.set_ticker("oadf");
	brc20.set_transfer_amount("20");
	brc20.set_inscribe_to(pubKey.bytes.data(), pubKey.bytes.size());
	auto& changeOut = *signing.add_outputs();
	changeOut.set_value(forFeeAmount);
	changeOut.mutable_builder()->mutable_p2wpkh()->set_pubkey(pubKey.bytes.data(), pubKey.bytes.size());
	Proto::SigningInput legacy;
	*legacy.mutable_signing_v2() = signing;
	Proto::SigningOutput output;
	ANY_SIGN(legacy, TWCoinTypeBitcoin);
	EXPECT_EQ(output.error(), Common::Proto::OK);
	ASSERT_TRUE(output.has_signing_result_v2());
	EXPECT_EQ(output.signing_result_v2().error(), BitcoinV2::Proto::Error::OK);
	EXPECT_EQ(hex(output.signing_result_v2().encoded()), "02000000000101089098890d2653567b9e8df2d1fbe5c3c8bf1910ca7184e301db0ad3b495c88e0100000000ffffffff02581b000000000000225120e8b706a97732e705e22ae7710703e7f589ed13c636324461afa443016134cc051040000000000000160014e311b8d6ddff856ce8e9a4e03bc6d4fe5050a83d02483045022100a44aa28446a9a886b378a4a65e32ad9a3108870bd725dc6105160bed4f317097022069e9de36422e4ce2e42b39884aa5f626f8f94194d1013007d5a1ea9220a06dce0121030f209b6ada5edb42c77fd2bc64ad650ae38314c8f451f3e36d80bc8e26f132cb00000000");
	EXPECT_EQ(hex(output.signing_result_v2().txid()), "797d17d47ae66e598341f9dfdea020b04d4017dcf9cc33f0e51f7a6082171fb1");
	// Successfully broadcasted: https://www.blockchain.com/explorer/transactions/btc/797d17d47ae66e598341f9dfdea020b04d4017dcf9cc33f0e51f7a6082171fb1
	}

You need to change the BRC20 Inscribe output to a regular P2WPKH here:

wallet-core/tests/chains/Bitcoin/TWBitcoinSigningTests.cpp

Line 449 in 7cd532c

auto& brc20 = *out.mutable_builder()->mutable_brc20_inscribe();