I have an image in signature. When sending from admin image is shown correctly and has attribute data-image-whitelisted. But when using API it is broken

$url = 'https://api2.frontapp.com/channels/' . $channel_id . '/messages';
$body = array(
'to' => array( $to ),
'subject' => $subject,
'body' => $content,
'text' => wp_strip_all_tags( $content ),
'options' => array(
'archive' => false,
),
'author_id' => 'tea_j7twg',
'signature_id' => $signature_id,
);
$args = array(
'method' => 'POST',
'headers' => array(
'Authorization' => 'Bearer ' . $api_token,
'Content-Type' => 'application/json',
// 'Content-type' => 'multipart/form-data',
),
'body' => wp_json_encode( $body ),
'timeout' => 30,
);

I know also that if omit author_id, email always in spam.