Failing to send SOL from PDA (bidding auction with escrow)

Question

I created an auction with escrow. I succesfully create a campaign account, and can do the first bid. But I try a second bid, the program should send the previous bid back to the previous bidder. Every time I try this I get this error:

Proxy {logs: Array(4), programErrorStack: wt, stack: 'Error: failed to send transaction: Transaction sim…id (webpack-internal:///./pages/index.jsx:110:13)', message: 'failed to send transaction: Transaction simulation…alances before and after instruction do not match'}
[[Handler]]
: 
Object
[[Target]]
: 
Error: failed to send transaction: Transaction simulation failed: Error processing Instruction 0: sum of account balances before and after instruction do not match at Connection.sendEncodedTransaction (webpack-internal:///../node_modules/@solana/web3.js/lib/index.browser.esm.js:7362:13) at async Connection.sendRawTransaction (webpack-internal:///../node_modules/@solana/web3.js/lib/index.browser.esm.js:7319:20) at async ct (webpack-internal:///../node_modules/@project-serum/anchor/dist/browser/index.js:59:9950) at async st.sendAndConfirm (webpack-internal:///../node_modules/@project-serum/anchor/dist/browser/index.js:59:8673) at async Object.eval [as bid] (webpack-internal:///../node_modules/@project-serum/anchor/dist/browser/index.js:74:48251) at async bid (webpack-internal:///./pages/index.jsx:110:13)
[[IsRevoked]]
: 
false

This is my program:

use anchor_lang::prelude::*;
use anchor_lang::solana_program::entrypoint::ProgramResult;

declare_id!("9V9FcjfsbLV1LD3n7GrdScf1pNh9ReUiRiWK12JKQjDu");

#[program]
pub mod crowdfunding {
    use super::*;

     pub fn create(ctx: Context<Create>, name: String, description: String, minimum: u64, delta: u64) -> ProgramResult {
        let campaign = &mut ctx.accounts.campaign;
        campaign.name = name;
        campaign.description = description;
        campaign.highest_bid = minimum;
        campaign.minimum = minimum;
        campaign.delta = delta;
        campaign.highest_bidder = *ctx.accounts.user.key;
        campaign.admin = *ctx.accounts.user.key;
        Ok(())
     }

     pub fn close(ctx: Context<Close>) -> ProgramResult {
        let campaign = &mut ctx.accounts.campaign;
        let user = &mut ctx.accounts.user;
        if campaign.admin != *user.key {
            return Err(ProgramError::IllegalOwner);
        }
        let rent_balance = Rent::get()?.minimum_balance(campaign.to_account_info().data_len());
        if **campaign.to_account_info().lamports.borrow() - rent_balance < campaign.highest_bid {
            return Err(ProgramError::InsufficientFunds);
                     
        }
        **campaign.to_account_info().try_borrow_mut_lamports()? -= campaign.highest_bid;
        **user.to_account_info().try_borrow_mut_lamports()? += campaign.highest_bid;
        Ok(())
     }

     pub fn bid(ctx: Context<Bid>, amount: u64) -> ProgramResult {
        let campaign = &mut ctx.accounts.campaign;

        let old_bid =  &campaign.highest_bid;
        let old_bidcopy = &campaign.highest_bid;
        let old_bidder = &mut ctx.accounts.old_bidder;


             if amount < ( campaign.highest_bid + campaign.delta ) {
            return Err(ProgramError::InsufficientFunds);
        }

       if  campaign.highest_bidder != *old_bidder.key {
             return Err(ProgramError::IllegalOwner);
       }



        if campaign.admin != *old_bidder.key {

            let rent_balance = Rent::get()?.minimum_balance(campaign.to_account_info().data_len());
            if **campaign.to_account_info().lamports.borrow() - rent_balance < campaign.highest_bid {
            return Err(ProgramError::InsufficientFunds);
                     
        }
        **campaign.to_account_info().try_borrow_mut_lamports()? -= *old_bid;
        **old_bidder.to_account_info().try_borrow_mut_lamports()? += *old_bidcopy ;
          
        }


        let ix = anchor_lang::solana_program::system_instruction::transfer(
            &ctx.accounts.user.key(),
            &ctx.accounts.campaign.key(),
            amount
        );
        anchor_lang::solana_program::program::invoke(
            &ix,
            &[
                ctx.accounts.user.to_account_info(),
                ctx.accounts.campaign.to_account_info()
            ]
        );

        (&mut ctx.accounts.campaign).highest_bid = amount;
         (&mut ctx.accounts.campaign).highest_bidder = ctx.accounts.user.key();
        Ok(())
     }

}

#[derive(Accounts)] 
#[instruction(name: String)]
pub struct Create<'info> {
    #[account(init, 
        payer=user, 
        space=1000, 
        seeds=[
            user.key().as_ref(),
            b"_",
            name.as_ref()
    ], bump)]
    pub campaign: Account<'info, Campaign>,
    #[account(mut)]
    pub user: Signer<'info>,
    pub system_program: Program<'info, System>

}

#[derive(Accounts)] 
pub struct Close<'info> {
    #[account(mut)]
    pub campaign: Account<'info, Campaign>,
    #[account(mut)]
    pub user: Signer<'info>

}

#[derive(Accounts)] 
pub struct Bid<'info> {
    #[account(mut)]
    pub campaign: Account<'info, Campaign>,
    #[account(mut)]
    pub user: Signer<'info>,
    /// CHECK We check it with campaign data
    #[account(mut)]
    pub old_bidder: AccountInfo<'info>,
    pub system_program: Program<'info, System>
}

#[account]
pub struct Campaign {
    pub admin:  Pubkey,
    pub highest_bidder: Pubkey,
    name: String,
    description: String, 
    minimum: u64,
    delta: u64,
    highest_bid: u64
}

I was also wondering: Who will pay for this transaction (send the SOL back). It should be the new bidder... Thank you very much for your time!

Answer 1

The answer to this question solved it for me:

Error processing Instruction 0: sum of account balances before and after instruction do not match

In my case I had a function that had two shipments of balances. One through the system program with transfer and another through try_borrow_mut_lamports()?.

You have to put the transfer function first and then the try_borrow_mut_lamports() function