Method: stickers.setStickerSetThumb

Set stickerset thumbnail

Parameters:

Name	Type	Description	Required
stickerset	InputStickerSet	Stickerset	Optional
thumb	MessageMedia, Update, Message or InputDocument	Thumbnail (only for normal stickersets, not custom emoji stickersets).	Optional
thumb_document_id	long	Only for custom emoji stickersets, ID of a custom emoji present in the set to use as thumbnail; pass 0 to fallback to the first custom emoji of the set.	Optional

Return type: messages.StickerSet

Can bots use this method: YES

MadelineProto Example (now async for huge speed and parallelism!):

if (!file_exists('madeline.php')) {
    copy('https://phar.madelineproto.xyz/madeline.php', 'madeline.php');
}
include 'madeline.php';

$MadelineProto = new \danog\MadelineProto\API('session.madeline');
$MadelineProto->start();

$messages_StickerSet = $MadelineProto->stickers->setStickerSetThumb(stickerset: $InputStickerSet, thumb: $InputDocument, thumb_document_id: $long, );