Creating Transaction with blockcypher API, Transaction new not found

I am new here and I am trying to create a bitcoin wallet with flutter, I have succeeded in creating address with private key, using bip32, but I am trying to create a transaction to send bitcoin with blockcypher API call, trying to create new transaction it give error 404 , {"error" Transaction new not found}, please can anyone help me with this issue. I am about to cry trying to to fix this issue.
Thanks

Why Can’t I Reverse secp256k1’s Public Key Point In Order To Determine The Private Key?

I understand that the public key q is generated by the point addition of g (some secp256 k1 constant) u times such that u is a big number (private key). This process can be simplified in this diagram below.

Hence the formula follows q=u*j

enter image description here
But why cant I use this diagram below and trace back the public key point to the point of the private key by following the tangents back to the original point. I’m sure I could do this in desmos-graphing or something using some pretty simple linear algebra.

Multisig with existing single sig + passphrase

If I take 2 brand new HW wallets (like a Coldcards), plus an existing hw single sig wallet that has a passphrase and finds already assigned to it (like a Trezor)and then create a new multisig 2 of 3 set up, will the passphrase be required to use the existing Wallet within the multisig (to send, for instance)?

If I don’t want the passphrase to be required, but have funds on the existing wallet already, how would I go about moving the funds and creating the multisig with these 3 wallets, where no passphrase is required for that existing wallet?

Hope this is clear and thank you.

SegWit signing algorithm and its improvement

I was reading about Segregated Witness upgrade from the book Mastering Bitcoin by Andreas and there were some questions I have not figured out. I am appreciated to get some of your help!

A) There was a passage of the book talking about SegWit helps reduce the complexity of the signing algorithm.

Segregated Witness upgrades the signature functions (CHECKSIG, CHECKMULTISIG,
etc.) to reduce the algorithm’s computational complexity. Before segwit, the algorithm used to produce a signature required a number of hash operations that was
proportional to the size of the transaction. Data-hashing computations increased
in O(n^2) with respect to the number of signature operations, introducing a substantial computational burden on all nodes verifying the signature. With segwit,
the algorithm is changed to reduce the complexity to O(n).

What is the original algorithm here whose complexity is O(n^2) (is it ECDSA or something else)? And also what is the new SegWit signing algorithm, and how it got the complexity of O(n)?

B) There was also a passage talking about SegWit improvement.

Segregated Witness signatures incorporate the value (amount) referenced by each
input in the hash that is signed. Previously, an offline signing device, such as a
hardware wallet, would have to verify the amount of each input before signing a
transaction. This was usually accomplished by streaming a large amount of data
about the previous transactions referenced as inputs. Since the amount is now
part of the commitment hash that is signed, an offline device does not need the
previous transactions. If the amounts do not match (are misrepresented by a
compromised online system), the signature will be invalid

What does it mean by saying Segregated Witness signatures incorporate the value (amount) referenced by each input in the hash that is signed. and Since the amount is now part of the commitment hash that is signed, an offline device does not need the previous transactions.? Does it mean that in Legacy block, the variable transfer value is not included in the hash, and now SegWit includes it?
And I cant understand how this make offline device not to need previous transactions’ info (although I do understand that every offline devices need previous utxo to sign a transaction)

bitcoin core 22.0 debug problem, and, berkeley version?

you know the problem of this sorti problem ? error and version berkeley ? please !

Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)

Using wallet C:…\wallet1.dat ( wallet.dat and the other wallet2.dat the same)

BerkeleyEnvironment::Open:LogDir:C:…\database ErrorFile:C:…\wallets\db.log

A error message ! …

what is the probleme here please ? thanks !