Thank you for your interest in Ubidots. Please keep in mind the Ubidots has the following structure:
Data Source or Sources = It is a equipment to transmit, can be a raspberry pi, arduino or other source that groups variables
Variable = It is a group of values in time that describe the physical phenomena you are measuring; like a temperature, humidity, energy, etc.
It seems that you are trying to send time-series values to your data source ID, not a variable. Your should click on the data source and then create a variable, then retrieve the ID of this variable.