Watch-only, balance not "available" for psbt #83

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Expected behavior

Be able to create a psbt with a watch-only balance.

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Actual behavior

Entering any amount yields an error message : "The amount exceeds your balance".

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To reproduce

• Created a new watch-only wallet with bitcoin-qt (with "disable private keys")
• Imported an address (segwit p2sh) in the console
• Rescanned the blockchain (in the console)
• Bitcoin-qt sees my "balance" in the "overview" screen and in the "send" screen (bottom-right corner of the send screen)
• In the send screen : if I click "Use available balance", the amount stays at zero.
• No coins shown in "Inputs" (coin control feature).
• I tried to send an amount that's less than my balance (in the address being watched in watch-only mode) but I only get the error message "The amount exceeds your balance". For example, trying to send 2000 sats with a low transaction fee (of 2123 sat/kB) on a watch-only balance of more than 50 000 sats.
• I do see the "create unsigned" button in the bottom-left corner.

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System information

Xubuntu 18.04.5 Bitcoin Core 0.20.1

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The error message may be misleading. Exactly how did you import the address? I suggest using importmulti, include the witnessscript and be sure to set keypool to true.

Thank you very much.

Exactly how did you import the address?

I used importaddress in the console: importaddress "3...." "label" false and then rescanned the blockchain from the relevant blockheight (rescanblockchain 600000). I thought maybe that was the cause (not a full rescan) so I later tried that as well.

My goal was to :

1. use an airgapped coldcard hardware wallet (without usb, with only a microSD) to produce addresses completely offline,
2. be able to watch them with bitcoin core, and
3. later be able to use bitcoin core (online) to do a psbt transaction for signature on the airgapped coldcard,
4. all without exporting-importing the xpub.

Unfortunately, I don't see any way to get the witness script directly from the coldcard. I see by your answer that I misunderstood what is necessary to construct the psbt. Thank you very much for your time answering my issue!

ping @achow101

Same as in https://github.com/bitcoin/bitcoin/issues/27659. I'm quite sure that this was solved by https://github.com/bitcoin/bitcoin/pull/26699 (which solved https://github.com/bitcoin/bitcoin/issues/26687).

Ping me otherwise and will give it a look.