A new deep-dive by a R.E. Howard scholar into the question: “Red Nails”: Did Howard Create the City of Xuchotl From a Real-Life Inspiration? The case is unproven one way or the other, but it’s an interesting and well-illustrated investigation, and touches on a comment he made to H.P. Lovecraft.
LibriVox has a free audiobook of the long tale, at around 3.5 hours depending on how you nudge the playback speed. See also my R.E. Howard audio books for Conan in story-world order, to see where this story fits in the Conan timeline.