I have been learning pyMTurkR because MTurkR and MTurkRGUI no longer work.  It has been challenging, but I finally have it working. . .mostly.  I am posting this comment primarily for myself because I know I will forget this solution one day, but I hope that it can also help others at some point.

When using the GrantBonus() command, following the instructions on the pyMTurkR documentation will give you an “Invalid Request” error.  This is because the instructions tell you to type the monetary amount as “.50” for example.  It will give you an error unless you put a 0 in the dollar amount place when paying in cents.  That is, “.50” should be entered as “0.50”.  Otherwise, it will give you the Invalid Request error.  Hope this helps someone – particularly myself in the future when I forget this!