How do you pay fee with solana adapter for backend transcation of sol

Question

What i am trying to do this create a transcation on backend( which have pk for my wallet ) set frontend wallet as fee payer sign that transcation and send it to frontend and only if end user signs the wallet , confirm the tx and send to blockchain, This is what i have tried so far:

  const walletToSendSol = new PublicKey(wallet);
const transferTransaction = new Transaction().add(
  SystemProgram.transfer({
    fromPubkey: payer.publicKey,
    toPubkey:walletToSendSol ,
    lamports: LAMPORTS_PER_SOL / 80,
  })
);
transferTransaction.recentBlockhash = (
  await connection.getLatestBlockhash()
).blockhash;
transferTransaction.feePayer = walletToSendSol;
transferTransaction.sign(payer);
return new NextResponse(
  JSON.stringify({
    tx: base58.encode(
      transferTransaction.serialize({
        requireAllSignatures: false,
      })
    ),
  })
);

End user:

 const fetchTx = await fetch(`/api/getTx?wallet=${publicKey}`);
const { tx } = await fetchTx.json();
const decodedTx = base58.decode(tx);
const transcation = Transaction.from(decodedTx);
transcation.feePayer = publicKey;
const signature = await signTransaction(transcation);

but once click approve on phantom wallet nothing happens

Answer 1

It doesn't appear that you're sending the transaction, just signing it. You can use sendTransaction(transaction, connection) from the useWallet() hook in wallet adapter to handle the flow of signing and sending with a user's wallet.

After sendTransaction() is called, it's good practice to run a confirmation to ensure it landed. You can do this with the following:

const signature = await sendTransaction(transaction, connection);

await connection.confirmTransaction(signature, "confirmed");

// can also do this
const block = await connection.getLatestBlockhash("confirmed");
const result = await connection.confirmTransaction(
  {
    signature,
    ...block,
  },
  "confirmed",
);

const error = result.value.err;
if (error) {
   throw Error(error.toString());
}