I'm using a Sendinblue SMTP into my PHP project and I want to send transactionals emails to a dynamic list of emails, the problem is that I have a syntax error when I'm using a variable instead a string. For example, this code works great:
    include 'Mailin.php';
    $mailin = new Mailin('senders@sender.com', 'key');
    $mailin->
    addTo(
        array(
                 'email1@email.com' => '', 'email2@email.com' => '', 'email3@email.com' => ''
            )
    )->
    setFrom('sender@sender.com', 'Test')->
    setReplyTo('sender@sender.com', 'Test')->
    setSubject('Example')->
    setText('Test')->
    setHtml($htmlContent);
    $res = $mailin->send();
    print_r($res);
But if I use a variable instead the Strings in "addTo Array" it shows syntax error, for example:
    $customers = '';
    foreach ($clientes as $customer) {
        for ($i=1; $i < 41; $i++) { 
            if ($customer['email'.$i]  != "" or $customer['email'.$i] != NULL) {
                $customers .= "'".$customer['email'.$i]. "' => '', " ; //for each customer's email add the email in " 'email@email.com' => '', " format
            }
        }
    }
    $customers = substr($customers, 0, -2); //removes last space and comma of the String
    include 'Mailin.php';
    $mailin = new Mailin('senders@sender.com', 'key');
    $mailin->
    addTo(
        array(
                 $customers
            )
    )->
    setFrom('sender@sender.com', 'Test')->
    setReplyTo('sender@sender.com', 'Test')->
    setSubject('Example')->
    setText('Test')->
    setHtml($htmlContent);
    $res = $mailin->send();
    print_r($res);
If I use the Print_r($customers) function it shows the exact string that I used in my first example, even if I use the code:
    $text = "'email1@email.com' => '', 'email2@email.com' => '', 'email3@email.com' => ''";
    if ($customers == $text) {
        print_r("Yes");
    }else{
        print_r("No");
    }
The result is "Yes", but when I use the variable in
    addTo(
        array(
                 $customers
            )
    )->
shows an error, but if I use the string directly the email is sent
    addTo(
        array(
                 'email1@email.com' => '', 'email2@email.com' => '', 'email3@email.com' => ''
            )
    )->
And I don't know why it shows error if the $customers variable has the string that is needed.
Do you know how to use the variable with the emails that I need to send?
 
    