multiple errors, php to mysql tutorial [duplicate]

*Warning: mysqli_stmt_bind_param() expects parameter 1 to be mysqli_stmt, null given in C:\Program Files\Ampps\www\danik php login system\include\funcs.inc.php on line 64

Warning: mysqli_stmt_execute() expects parameter 1 to be mysqli_stmt, null given in C:\Program Files\Ampps\www\danik php login system\include\funcs.inc.php on line 66

Warning: mysqli_stmt_get_result() expects parameter 1 to be mysqli_stmt, null given in C:\Program Files\Ampps\www\danik php login system\include\funcs.inc.php on line 68

Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, null given in C:\Program Files\Ampps\www\danik php login system\include\funcs.inc.php on line 72*

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code below, can you please provide error correction and point me in the right direction to learn why this happened?

// create the functions we've referenced


// checks for empty fields
function emptyInputSignup($name, $username, $email, $password, $password_repeat) {
    $result; // declared here so we don't have to declare it in each if/else stmt
    if (empty($name) || empty($username) || empty($email) || empty($password) || empty($password_repeat)) {
        $result = true; // true means it's empty
    }
    else {
        $result = false; // our desired outcome
    }
return $result;
}

// invalid userID
function invalidUID($username) {
    $result;
    if (!preg_match("/^[a-zA-Z0-9]*$/", $username)) {
        $result = true;  // if doesn't contain the correct characters, return true, invalid username
    }
    else {
        $result = false;        
    }
return $result;
}

function invalidEMAIL($email) {
    $result;
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $result = true;
    }
    else {
        $result = false;        
    }
return $result;
}
// true = improper

// if they're not the same input
function passwordMATCH($password, $password_repeat) {
    $result;
    if ($password !== $password_repeat) {
        $result = true;
    }
    else {
        $result = false;        
    }
return $result;
}

    // checks if email and username taken
function uidEXISTS($conn, $username, $email) {
    $sqlsearch = "SELECT * FROM users WHERE usersID = ? OR usersEMAIL = ?;"; // the ? is a placeholder
    $stmt = mysqli_stmt_init($conn); // begins the prepared statement, we need to give $conn
    // allows stmt to use the prepared sqlsearch statement, preventing sql injection attacks
    if (!mysqli_stmt_prepare($stmt, $sqlsearch))// if the stmt fails and doesn't accept sql input
        header("location: ../signup.php?error=invalidEMAIL");
        exit();
}

    // if doesn't fail, use this
    mysqli_stmt_bind_param($stmt, "ss", $username, $email); // prepared statement, what kind of data are we submitting? two strings = ss
    // this user data is now bound to the user
    mysqli_stmt_execute($stmt); // executes the sql stmt
    // obtains info from the db
    $resultData = mysqli_stmt_get_result($stmt); // all the information we're binding and results we're getting, goes into $stmt

    // checks to see if $stmt contains info

    if ($row = mysqli_fetch_assoc($resultData)) { // $row returns true if data in here; data is in associative array in var $row
        return $row; // return all the info from inside the db
        // if data already exists inside the db, logs the user in using this data
}
    else {
        $result = false; // if not data returned from the db, false
        return $result;
}
    mysqli_stmt_close($stmt);

function createUSER($conn, $name, $username, $email, $password) { // instead of checking against the db, use this to sign up user
    // creates user
    $sqlsearch = "INSERT INTO users (usersNAME, usersUID, usersEMAIL, usersPASSWORD) VALUES (?, ?, ?, ?);";
    // have to be in proper order
    $stmt = mysqli_stmt_init($conn);

    if (!mysqli_stmt_prepare($stmt, $sqlsearch)) { //always check if fails
        // if error, it'll send us back to signup page with error message
        header("location: ../signup.php?error=statementfailed");
        exit();
    }

    $hashedpwd = password_hash($password, PASSWORD_DEFAULT); // auto-updated & built-in php func()

    mysqli_stmt_bind_param($stmt, "ssss", $name, $username, $email, $hashedpwd); // what are we submitting to php?, $stmt, "s" means two strings;
    mysqli_stmt_execute($stmt);
    mysqli_stmt_close($stmt);

    header("location: ../signup.php?error=none"); // go here after signing in
    exit();
}```