Cross-program invocation with unauthorized signer or writable account: Solana Tip Program

I'm building a Solana Anchor program for a tipping dApp, but I'm encountering an error. Can anyone assist me in troubleshooting and fixing the give_tip function?"

use anchor_lang::{    prelude::*,    solana_program::{        program::invoke, system_instruction::create_account, system_instruction::transfer,    },};// use anchor_lang::system_program::{create_account, CreateAccount};declare_id!("5bZeT4cdAQH8dN2WW9s2kdzMzxy5oJX4hTProBaSazEn");pub const PROGRAM_PUBKEY: &str = "program_seed";pub const TIP_SEED: &str = "tip";#[error_code]pub enum TipError {    #[msg("The tip has already been claimed.")]    AlreadyClaimed,}#[program]mod tip {    use super::*;    pub fn init(_ctx: Context<InitMaster>) -> Result<()> {        Ok(())    }    pub fn give_tip(ctx: Context<GiveTip>, amount: u64) -> Result<()> {        let tip = &mut ctx.accounts.tip;        let sender = &ctx.accounts.sender;        let system_program = &ctx.accounts.system_program;        let pub_key = &tip.key();        msg!("Program invoked. Creating a system account...");        msg!("New public key will be: {}", tip.key().to_string());        // Ensure the tip hasn't been claimed already        if tip.amount > 0 {            return Err(TipError::AlreadyClaimed.into());        }        // The minimum lamports for rent exemption        let lamports = (Rent::get()?).minimum_balance(0);        msg!("Minimum lamports for rent exemption: {}", lamports);        invoke(&create_account(sender.key, pub_key, lamports, 0, system_program.key),&[                sender.to_account_info(),                tip.to_account_info(),                system_program.to_account_info(),            ],        )?;        msg!("Account created successfully.");        // Transfer SOL to Tip PDA        invoke(&transfer(&sender.key(), &tip.key(), amount),&[                sender.to_account_info(),                tip.to_account_info(),                ctx.accounts.system_program.to_account_info(),            ],        ).map_err(|e| {            msg!("Error transferring SOL: {}", e);            e        })?;        tip.amount = amount;        Ok(())    } }#[derive(Accounts)]pub struct InitMaster {}#[derive(Accounts)]#[instruction(receiver:Pubkey,amount: u64)]pub struct GiveTip<'info> {    #[account(      init_if_needed,     payer = sender,     space = 8 + 32 + 8 + 1,     seeds = ["program_seed".as_bytes(), &receiver.to_bytes() ,"tip".as_bytes()],     bump, )]    pub tip: Account<'info, Tip>,    #[account(mut)]    pub sender: Signer<'info>,    pub system_program: Program<'info, System>,}#[account]pub struct Tip {    pub to: Pubkey,    pub amount: u64,}