How to send thumbnails when using sendMediaGroup with multiple InputMediaAudio?

[ARKbr]

Im sending some music albuns using the method sendMediaGroup, i have tried many ways to add the thumbnail, but it does not show on telegram desktop (if i use the sendAudio method, it works fine)

const mediaGroup = []
mediaGroup.push({
    type: 'audio',
    media: {
        source: path.resolve(directory, mp3File),
        filename: mp3File
    },
    title: trackTitle,
    performer: trackArtist,
    duration: trackBd.duration,

    // thumbnail: 'cover.jpeg',    
    // thumb: { source: 'cover.jpeg' },
    // thumbnail: `attach://${photo.photo[0].file_id}`, // file sended by sendPhoto method
    // thumbnail: { type: 'photo', media: { source: `attach://${photoooo.photo[1].file_id}` } },
    // thumbnail: `attach://cover.jpeg`,

})

await bot.telegram.sendMediaGroup(
    chat_id,
    mediaGroup,
)

The documentation says:

Optional. Thumbnail of the file sent; can be ignored if thumbnail generation for the file is supported server-side. The thumbnail should be in JPEG format and less than 200 kB in size. A thumbnail's width and height should not exceed 320. Ignored if the file is not uploaded using multipart/form-data. Thumbnails can't be reused and can be only uploaded as a new file, so you can pass “attach://<file_attach_name>” if the thumbnail was uploaded using multipart/form-data under <file_attach_name>.

But i cant understand how can i use the “attach://<file_attach_name>” string

if i add a file of type 'photo' to the mediaGroup array, telegram trows an error 'you cant mix other file types with "audio"'

[MKRhere]

This is a bug. Will publish fix with the upcoming release.

[MKRhere]

Fixed and published to npm as release candidate 4.16.0-rc.2. Stable release when #1949 is merged.