Where's the dictation button?
Short answer: Unfortunately, Apple does not provide a way for us to make this feature accessible from our keyboard.
Long answer: Apple does not allow third-party keyboards to access the microphone, presumably because they are concerned about privacy. But leaving aside the fact that they let all manner of NON-keyboard apps access the microphone, they could also make dictation possible by providing an API for this directly rather than having the keyboard record the text first. Why they don't do this is uncertain.
If you'd like to see microphone support in PadKeys or any other third-party keyboard, please let Apple know.