Opening such a link prompts the user to choose a specific chat and opens the attachment menu in that chat. If the bot wasn't already added to the attachment menu, the user will be prompted to do so. You can specify which types of chats the user will be able to choose from. It can be one or more of the following types: users, bots, groups, channels separated by a + sign. If a non-empty startattach parameter was included in the link, it will be passed to the Mini App in the start_param field and in the GET parameter tgWebAppStartParam.