Pass fix value to query

I am trying to pass a value of my fix to my query but at the moment of doing it it says to me:

  

Array to string conversion

My fix comes from a function in a file called functions.php

It is the first value of my array that I want to pass to the query of my functions.php file

I have a variable that collects the result of my main function:

$emit = obtener_mensajes($conexion, $us);

This is where I want to insert my query and the variable:

<?php 

$query = "SELECT * FROM messages WHERE idEmitter IN ($us, $emit[0]) AND idReceiver IN ($emit[0], $us) ORDER BY sent ASC" ;

$run = $conexion->query($query);

while ($row = $run->fetch(PDO::FETCH_ASSOC)):
    //var_dump($row);

?>

This is my arrangement

array(1) {
  [0]=>
  array(10) {
    ["idEmitter"]=>
    string(1) "1"
    [0]=>
    string(1) "1"
  }
}