Если на каждый номер планируется отправлять отдельную картинку в сообщении, то в этом случае необходимо либо передавать полный http(s)-адрес внешнего файла в виде <file http(s)://...>, or send an additional fileurl parameter in the request that contains the full http(s) address of the image. When using fileurl, passing the mes parameter in the request is optional.
If, when creating a mailing list, one text is supposed to be sent to several numbers, then you need to insert the full http(s) link of the previously uploaded image file into the message text, which you can find out in your personal account on the sending page by clicking "attach file"-"Uploaded files". The attached file must not exceed 512 Kb in size and must meet one of the following formats: JPG, GIF, PNG.
Sending images