Splunk is complaining that there is a key under a header that it does not recognize. Briefly looking at inputs.conf reference manual for 7.3.1 (here) you can see that neither [input_http] nor python.version are recognized by that version of Splunk. The reason your input is not working is most likely due to being placed under a header that Splunk does not know what it means for inputs.conf (the python.version invalid key is most likely not the source of the issue, it would most likely be ignored).
Splunk uses the Python 3 interpreter by default so there's no need to specify it (as well as the fact that in inputs.conf, there is no key for "python.version").
If you are trying to enable a HTTP Event Collector Input, use the settings shown under this category.