Getting Error processing Instruction 0: Cross-program invocation with unauthorized signer or writable account

Question

I tried creating a PDA for my escrow program but I keep running into the error above. I ensured the seeds used in my testing code FindProgramAddress and the rust file are the same, but I still get this error. Does anyone know why? Should I be using uft8 encode for the seeds? My code is as such:

#[derive(Accounts)]
#[instruction(application_idx: u64, bump: u8)]
pub struct InitNewExchange<'info> {
    //Derived PDAs (Must specify seed and bump for PDA) 
    #[account(
        init, //Initializing a new account
        payer = user_sending,
        space = Exchange::LEN,
        seeds = [b"exchange",  
                user_sending.key.as_ref(),],
                
        bump,
    )]
    application_exchange: Account<'info, Exchange>,

    #[account(
        init, //Initializing a new account
        payer = user_sending,
        seeds = [b"wallet", 
                user_sending.key.as_ref(),],
        bump,
        token::mint =  mint_of_token_being_sent,
        token::authority = application_exchange,
    )]
    //Should not be signer or writable
    escrow_wallet_exchange: Account<'info, TokenAccount>,

    //User Accounts
    #[account(mut)]
    user_sending: Signer<'info>,
    ///CHECK: Not dangerous
    #[account(mut)]
    user_receiving: AccountInfo<'info>,
    #[account(mut)]
    mint_of_token_being_sent: Account<'info, Mint>,

    //Token wallet that escrow wallet has alredy approved
    #[account(
        mut,
        constraint = wallet_to_withdraw_from.owner == user_sending.key(),
        constraint = wallet_to_withdraw_from.mint == mint_of_token_being_sent.key(),
    )]
    wallet_to_withdraw_from: Account<'info, TokenAccount>,

    //App level accounts
    system_program: Program<'info, System>,
    token_program: Program<'info, Token>,
    rent: Sysvar<'info, Rent>,
}

and my test code:

let pda: PDAParams;

  //FUNCTIONS to prepare cross program invocation
  const getPDAparams = async(
    connection: anchor.web3.Connection, 
    sender?: anchor.web3.PublicKey,
    receiver?: anchor.web3.PublicKey,
    token?: anchor.web3.PublicKey): Promise<PDAParams> => {
    //Get timestamp for transaction
    const uid = new anchor.BN(parseInt((Date.now() / 1000).toString()));
    const uidbuffer = uid.toBuffer("le", 8);

    //findProgramAddress: 
    //Takes in seeds and program ID
    //Return a public key of PDA and checks that the pubkey is on the ed25519 curve
    let [exchangePubKey,] = await anchor.web3.PublicKey.findProgramAddress(
      [
        utf8.encode("exchange"), 
        sender!.toBuffer(), 
      ],
      program.programId,
    );

    let [walletPubKey,] = await anchor.web3.PublicKey.findProgramAddress(
      [
        utf8.encode("wallet"), 
        sender!.toBuffer(), 
      ],
      program.programId,
    );

    return {
      escrowWalletKey: walletPubKey,
      exchangeKey: exchangePubKey,
      idx: uid,
    }
  }

it("Initialize a payment by sender1", async() => {
        const amount = new anchor.BN(20000000);

        //Initialize mint and fund the account
        const tx1 = await program.methods
        .initNewExchange(pda.idx, amount)
        .accounts({
            applicationExchange: pda.exchangeKey,
            escrowWalletExchange: pda.escrowWalletKey,
            userSending: sender.publicKey,
            userReceiving: receiver.publicKey,
            //Account data type of mint
            mintOfTokenBeingSent: mintAddress,
            //Wallet of sender for that particular token
            walletToWithdrawFrom: senderWallet,
            systemProgram: anchor.web3.SystemProgram.programId,
            tokenProgram: spl.TOKEN_PROGRAM_ID,
            rent: anchor.web3.SYSVAR_RENT_PUBKEY,
        })
        .signers([sender])
        .rpc();

        console.log("Initialized a new exchange instance! 20 tokens being paid");

Any help is greatly appreciated!

Answer 1

The error

Cross-program invocation with unauthorized signer or writable account

is usually caused by one of two things

• you have not set the account to mut
• you haven't used the correct seeds for the account