Error Code: AccountDidNotSerialize. Error Number: 3004. Error Message: Failed to serialize the account

Question

I am trying to update value of string. I can update if its type is u8, u32, u64, or i64 but cannot update if it's a string type. Any guesses what am I doing wrong?

Code snippet:

1. Program Function

    pub fn set_uri(
        ctx: Context<ModifyLedger>,
        new_uri: String,
    ) -> Result<()> {
        let ledger_account = &mut ctx.accounts.ledger_account;
        ledger_account.uri = new_uri;    
        Ok(())
    }

2. derive Account:

#[derive(Accounts)]
pub struct ModifyLedger<'info> {
    #[account(mut)]
    pub ledger_account: Account<'info, Ledger>,
    #[account(mut)]
    pub wallet: Signer<'info>,
}

3. Account:

#[account]
pub struct Ledger {
    pub uri: String,
}

Answer 1

I increased the space of my account and redeployed the programs with new keys.

#[account(
  init,
  payer = payer,
  space = 82+36,
  seeds = [b"my_custom_seed"],
  bump)
 ]    
 pub ledger_account: Account<'info, Ledger>

Answer 2

Instead of this

#[account]
pub struct Ledger {
    pub uri: String,
}

use

// Implements an Accounts deserializer on the given struct.   
#[derive(Accounts)]
pub struct Ledger {
    pub uri: String,
}

Answer 3

Space was the issue for me as well. In my case, I solved it with the equivalent of the following

#[derive(Accounts)]
#[instruction(new_uri: String)]
pub struct ModifyLedger<'info> {
    #[account(
        mut,
        // 8 for discriminator, 4 for the string length, and uri.len() for the content of string
        space = 8 + 4 + new_uri.len() 
    )]
    pub ledger_account: Account<'info, Ledger>,
    
    #[account(mut)]
    pub wallet: Signer<'info>,
}

Essentially, I am computing the space required to store the ledger account struct, from the data passed in to the instruction. Remember to add 8 bytes at the start for anchor's discriminator.

#[account]
pub struct Ledger {
    pub uri: String,
}

Using the exact space required helps you be more efficient in terms of SOL usage.

References:

1. Solana Quick Start Tutorial - Program Derived Address - Implement Create Instruction (open the Explanation accordion)