startParameter property
Optional. Deep-linking parameter for the /start message sent to the bot when a user presses the button. 1-64 characters, only A-Z, a-z, 0-9, _ and - are allowed.
Example: An inline bot that sends YouTube videos can ask the user to connect the bot to their YouTube account to adapt search results accordingly. To do this, it displays a 'Connect your YouTube account' button above the results, or even before showing any. The user presses the button, switches to a private chat with the bot and, in doing so, passes a start parameter that instructs the bot to return an OAuth link. Once done, the bot can offer a switch_inline button so that the user can easily return to the chat where they wanted to use the bot's inline capabilities.
Implementation
final String? startParameter;