Not a lot of info here, presumably the error occurs while building the custom recipe.
There is a 'hostpython3' recipe there, perhaps your custom recipe is from back in the Python2 days and must be updated?
Buildozer/p4a no longer use Python2.
Obviously that is just a guess.
Custom recipe users have to be self supporting, requests for (re-)writing custom recipes generally go unanswered both here and on Discord.