Error while sending an Instruction in Android (Kotlin): Cross-program invocation with unauthorized signer or writable account

Question

I am getting some error while sending a transaction in Android (Kotlin)

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

This is the function which is creating the Instruction Object.

public fun createQuestion(author: PublicKey, question: String): TransactionInstruction {
        val keys = mutableListOf<AccountMeta>()
        keys.add(AccountMeta(getQuestionPda().address, false, true))
        keys.add(AccountMeta(getProgramInfoPda().address, false, true))
        keys.add(AccountMeta(author, true, true))
        keys.add(AccountMeta(SystemProgram.PROGRAM_ID, false, false))
        return TransactionInstruction(PublicKey(BuildConfig.PROGRAM_ID), keys,
            Borsh.encodeToByteArray(AnchorInstructionSerializer("create_question"), Args_createQuestion("Android Question")))
}

PS: Typescript Tests are working, I had one more Instruction in Android which is also working.

This is the structure for this instruction:

{
      "name": "createQuestion",
      "accounts": [
        {
          "name": "question",
          "isMut": true,
          "isSigner": false
        },
        {
          "name": "programInfo",
          "isMut": true,
          "isSigner": false
        },
        {
          "name": "author",
          "isMut": true,
          "isSigner": true
        },
        {
          "name": "systemProgram",
          "isMut": false,
          "isSigner": false
        }
      ],
      "args": [
        {
          "name": "content",
          "type": "string"
        }
      ]
    }

This is the Anchor Instruction:

#[derive(Accounts)]
#[instruction(content: String)]
pub struct CreateQuestion<'info> {
    #[account(
        init_if_needed, 
        payer = author, 
        space = Question::LEN + content.len(), 
        seeds = [b"question", program_info.question_count.to_be_bytes().as_ref()],
        bump
    )]
    pub question: Account<'info, Question>,

    #[account(mut)]
    program_info: Account<'info, ProgramInfo>,

    #[account(mut)]
    pub author: Signer<'info>,

    pub system_program: Program<'info, System>,
}

I have already tried:

• Writing the anchor program again and redeploying.
• Ran typescript tests to check if they were working (and they are)
• Used a new keypair to sign transactions in typescript (still working)

Note: InitializeProgramInfo instruction is working in Android. Only CreateQuestion is not working.

This is the instruction for Create Question

pub fn create_question(ctx: Context<CreateQuestion>, content: String) -> Result<()> {

    require!(content.chars().count() < 30, QuestionError::QuestionTooLong);
    require!(content.chars().count() > 1, QuestionError::QuestionEmpty);

    let clock: Clock = Clock::get().unwrap();

    ctx.accounts.question.set_inner(
        Question::new(
            ctx.accounts.author.key(),
            clock.unix_timestamp,
            content,
            ctx.accounts.program_info.question_count,
            0,
            *ctx.bumps.get("question").unwrap()
        )
    );

    ctx.accounts.program_info.increment_question_count();

    Ok(())
}

Answer 1

As described in the comments this error can have many different causes.

• An account that needs to be a signer didn't sign
• An account that is being changed is not marked as mutable
• The PDA address is derived differently in the program and in the client

So here the PDA derived in the kotlin sdk was not the same as in the anchor program.