We typically calculate payback period using all go to market costs (sales + marketing + CS), but not product development or any COGS (which includes things like AWS costs).
Again, it's not a management report. You should use it for prioritisation. For example, all our go-to-market is very country-specific. So we can look at the payback period for different countries and compare how well they are performing, and that tell us which ones we should invest more into.
Every business should do it differently, based on which expenses are fixed or variable for them.
