Unable to use the bot

Hello, Good Morning

Today I was developing the assignment bot, but in sandbox mode I got a message that said: ‘‘Incorrect Bot ID’’ when I was in the Studio option
I gave it Configure, Reset Bot, and now the Sandbox mode option appears in gray.

The following appears on the screen:

If the welcome message is not configured, try setting the same and check the direct link.

Configure the fallback message in “home section” then issue will be resolved @Sagar