Shiny / R：从字符日期格式化图表日期

I have spent hours on this and I am a new user. I've been to many websites and tried different things. I can not seem to get the graph to show dates in a YYYY-MM format on the x axis. The date starts out being character, which seems to work for the date range inputs. But the graph date is either showing as a long number or as Mar-01, Apr-01, etc. I'd rather see 2017-Feb, 2017-Mar, 2017-Apr, 2017-May. IF they would not sort appropriately like this I would need 2017-02, 2017-03, etc. (or even 201702 - just some year then month format). My app has several dynamic UI, which are working. What I'm showing is a simple version but I left the date range pick in just in case that is relevant. I have spent hours on this and I am a new user.