Error while using decompose and stl functions in R
The error is likely due to the fact that your x is an irregular time series: there are temporal gaps, e.g. no data on 2015-01-03, 2015-01-04. You will have to implement your own version of decompose, e.g. following this approach:

https://stackoverflow.com/questions/12623027/how-to-analyse-irregular-time-series-in-r