ctx.accounts.position_account.amount = position_size - user_pays;
require!(
      ((amt as u128)
      .checked_mul(ctx.accounts.trading_pool.max_borrow as u128).expect("overflow")
      .checked_div(10_u128.pow(ctx.accounts.mint.decimals as u32))).expect("overflow") as u64
       >= ctx.accounts.position_account.amount, 
      FlashFillError::ExpectedCollateralNotEnough);
