Thanks for following up, @SamuelSMendes. I'm glad to hear you are having some progress. There are a few older Discuss and StackOverflow posts that may be useful to take a look at:
- Watcher with Index Action - Not writing data properly
- mustache - Use input ElasticSearch document fields in Watcher fields - Stack Overflow
This guide has also been helpful for me to take a look at in the past as well.