First evidence of cacao use dates from approximately 5,300 years ago by the Mayo-Chinchipe civilization in Ecuador.  Traces of theobromine, which is a chemical compound in cacao, have been found in their pottery at an Ecuadorian dig site called Santa Ana-La Florida. This is a recent discovery. Up until 2018 it was believed that the earliest cacao use was about 4000 years ago by the pre-Olmec peoples of what is now Tabasco in Mexico. It seems as if a civilization in South America was the first to use cacao since cacao originated in the Amazon basin. From here, they were probably transported to Soconusco in Chiapas. 

(Source: https://goodnowfarms.com/a-brief-history-of-cacao/)