PHP mysqli prepare statement bind_param boolean error - php

Question

Testing the statement from all side, but failed to find a solution for it.
// Insert the new user into the database
if( $insert_stmt = $mysqli->prepare("INSERT INTO client (username, email,
password, reg_ip, salt, country, ref_id, pin, ref_by, ref_by_2) VALUES ( ?,
?, ?, ?, ?, ?, ?, ?, ?, ?)")){
$insert_stmt->bind_param("ssssssssii", $username, $email, $pass_2,
$reg_ip, $random_salt, $countryname, $ref_code, $hashed_pin, $user_id3,
$user_id4);
$insert_stmt->execute();
This never executes or gets inside the if statement.
I debugged it by removing the if part, that shows bind_param() is boolean error.
$insert_stmt = $mysqli->prepare("INSERT INTO client (username, email,
password, reg_ip, salt, country, ref_id, pin, ref_by, ref_by_2) VALUES ( ?,
?, ?, ?, ?, ?, ?, ?, ?, ?)");
$insert_stmt->bind_param("ssssssssii", $username, $email, $pass_2, $reg_ip,
$random_salt, $countryname, $ref_code, $hashed_pin, $user_id3, $user_id4);
if($insert_stmt->execute()){
Fatal error: Call to a member function bind_param() on boolean
I have done following test:
All 10 variables data type test = OK (with gettype() function)
Variables data value = OK (printed all data value for checking)
Mysql query statement = OK (tested on MYSQL directly with inputted data, mysql is inserting values)
There is no syntax error either.
Variable alignment is = Ok
Data connection is = ok (as it runs other prepare statements without errors on same page)
Then where is the mistake?

Answer 1

I figure it out.
Solution:
It was not working because of the previous prepare statement $stmt_aff connection was not closed.
Once I closed it. Next Prepare statement $insert_stmt started working.
A good lesson learned why bind_param boolean error get produced if there are multiple prepare statement on the same page.
$stmt_aff->close();