Bid PSBT

If you would like to manually construct bid transactions, you can use the Spaces Wallet CLI to get the bid contract signature for the auctioned space output, total burned and other details: $ space-cli getspace myspacename

The bid PSBT spends an auctioned space output and refunds the previous bidder's burned coins. Bid PSBTs must follow the exact structure defined here otherwise it would not be possible to re-construct it from the compressed form:

Field	Value
Version	2
Lock Time	0

Input

Field	Value
Previous Output	prev_txid:prev_index
Sequence	0xFFFFFFFD
Sighash type	SINGLE|ANYONECANPAY

Output

Field	Value
Script Pubkey	prev_script_pubkey
Value	total_burned + prev_value

Where:

• prev_txid:prev_index refers to the transaction ID and output index of the previous auctioned space UTXO.

• total_burned is the total amount of coins burned during the auction until this point.

• prev_value is the value of the previous output (prev_txid:prev_index)

• prev_script_pubkey the exact p2tr script pubkey of (prev_txid:prev_index)

Compressing Bid PSBT to 65 bytes

In this example, the Space UTXO would be identified with the outpoint #f9395e:6

To fit the PSBT into a single OP_RETURN (80-byte limit), we:

1. Omit known details (tx version, input sequence, lock time).

2. Use transactions with at least two unspent outputs for auctions (these outputs must be tracked by the protocol).

3. Encode information in this format:

Inputs	Outputs
Previous Output: prev_txid:prev_index	Script Pubkey: OP_RETURN OP_PUSHBYTES_65 prev_index_2:64-byte sig Value: bid_increment

Where:

• prev_txid: Transaction ID containing the UTXO to be auctioned

• prev_index: Any output index from prev_txid (references the transaction)

• prev_index_2: Index of the output to be auctioned (1 byte)

• 64-byte sig: Schnorr signature

• bid_increment: The current bid increment which equals the bid amount minus the total burned in prior bids and must be greater than zero

Total size: 65 bytes (1 byte + 64 bytes), fitting within the OP_RETURN limit.