OptionalplaceholderThe placeholder to be shown in the input field when the keyboard is active; 1-64 characters.
OptionalselectiveUse this parameter if you want to show the keyboard to specific users only. Targets: 1) users that are
in the text of the Message object; 2) if the bot's message is a reply (has reply_to_message_id), sender of the original message.
Example: A user requests to change the bot's language, bot replies to the request with a keyboard to select the new language. Other users in the group don't see the keyboard.
OptionalsingleRequests clients to hide the keyboard as soon as it's been used. The keyboard will still be available, but clients will automatically display the usual letter-keyboard in the chat – the user can press a special button in the input field to see the custom keyboard again.
Readonlytype
Force the user to send a reply