I want to convert PaymentExtendedSigningKeyShelley_ed25519_bip32 to PaymentSigningKeyShelley_ed25519,but I have a problem

I want to convert PaymentExtendedSigningKeyShelley_ed25519_bip32 to PaymentSigningKeyShelley_ed25519:

1、
skey generated by mnemonic:

{
    "type": "PaymentExtendedSigningKeyShelley_ed25519_bip32",
    "description": "",
    "cborHex": "5880084dd7af554b9c8c7e5a777dc528ed570cfd36db32bc2be359cc208dc947a94333daaf32256a61be975d1f7908a50ebfae96459309906f7ec40b1969450137bd40d883805bb6dca9bdbba85afbc6556b34447c9ddec81f463924b4a2b711128ecd3aca54d3b1f34613d9f54224a1a6d2369e4f3cfb8d67ae342b33ee3692dffb"
}

Send transaction: ok

The cborhex here contains of 4 parts:

  1. prefix 5880 - bytestring of 128 bytes
  2. signing key (64 bytes) - b0bf46232c7f0f58ad333030e43ffbea7c2bb6f8135bd05fb0d343ade8453c5eacc7ac09f77e16b635832522107eaa9f56db88c615f537aa6025e6c23da98ae8
  3. verification key (32 bytes) - fbbbf6410e24532f35e9279febb085d2cc05b3b2ada1df77ea1951eb694f3834
  4. chain code (32 bytes) - b0be1868d1c36ef9089b3b094f5fe1d783e4d5fea14e2034c0397bee50e65a1a

==》 According to the above description I can get:

58+80+
084dd7af554b9c8c7e5a777dc528ed570cfd36db32bc2be359cc208dc947a943+33daaf32256a61be975d1f7908a50ebfae96459309906f7ec40b1969450137bd (signing key:why 64 bytes ?)
+40d883805bb6dca9bdbba85afbc6556b34447c9ddec81f463924b4a2b711128e (verification key)
+cd3aca54d3b1f34613d9f54224a1a6d2369e4f3cfb8d67ae342b33ee3692dffb (chain code)

===>

58+40+084dd7af554b9c8c7e5a777dc528ed570cfd36db32bc2be359cc208dc947a94333daaf32256a61be975d1f7908a50ebfae96459309906f7ec40b1969450137bd
or
Since the signing key is 64bytes, I saw that some answers take the first 32bytes, so I can get:
58+20+084dd7af554b9c8c7e5a777dc528ed570cfd36db32bc2be359cc208dc947a943

Send transaction: false MissingVKeyWitnessesUTXOW

I want skey to remain the same as cardano-cli address key-gen(58203dda306bdc93da8d8fb9c4dbf0ef9bc0c7d4283eee5b962a34b5c8e1c4c43b61)

2、

cardano-cli address key-gen \
--verification-key-file payment1.vkey \
--signing-key-file payment1.skey
{
    "type": "PaymentSigningKeyShelley_ed25519",
    "description": "Payment Signing Key",
    "cborHex": "58203dda306bdc93da8d8fb9c4dbf0ef9bc0c7d4283eee5b962a34b5c8e1c4c43b61"
}

Send transaction: ok

58+20+
3dda306bdc93da8d8fb9c4dbf0ef9bc0c7d4283eee5b962a34b5c8e1c4c43b61 (32 bytes)