Header reply_to_list does not seem to work in PHP

[NoudL]

Hi,

I'm trying to add multiple replyTo's to an Mail object. I see that the replyToList is not fully implemented in the PHP version but it's mentioned to use the 'reply_to_list' header: https://docs.sendgrid.com/api-reference/mail-send/mail-send#multiple-reply-to-emails

Now I cannot get this to work. What syntax does this list need to be? Because I cannot get it working.
I've tried:

$email->addHeader('reply_to_list', "email1@email.com, email2@email.com");
$email->addHeader('reply_to_list', "[email1@email.com, email2@email.com]");
$email->addHeader('reply_to_list', "[{'email': 'email1@email.com'}, {'email': 'email2@email.com'}]");

and used json_encode to convert an object containing 'email => "email@email.com"', but none of these seem to work.

I realize in the future something like addReplyTo or setReplyToList will be supported, but I have to implement something now.

I'm using "sendgrid/sendgrid": "~7" in composer.

Any help is appreciated.