Please note that ResearchGate is neither a journal nor a publisher, you cannot "publish" a paper here. It is a platform for papers published in journals, or to present unpublished texts, data etc. See also "Is ResearchGate a publisher?" in https://help.researchgate.net/hc/en-us/articles/14292596164753. And see this help page for instructions how to add published or unpublished research to ResearchGate: https://help.researchgate.net/hc/en-us/articles/14293005132305-How-to-add-research
Following on from the comment by Dr Wolfgang R. Dick , I would suggest that if you are seeking publication (and official recognition of this externally), that you would have to find a suitable journal and ensure you fit their requirements (eg word count, number of references etc)