Other than a missing function, is there anything else that would cause this error?

** (UndefinedFunctionError) function :pg2.create/1 is undefined or private

pg2 has been deprecated and removed from recent Erlang versions. Whatever lib you are using that uses pg2 needs to be updated to use the new pg.

This is an old ap, running on 1.13.2-otp-24.
Updating will likely break something else.

Module pg was introduced in OTP 23.0.

so either, you’re adding a new dependency that needs to run on otp 23 or lower. or you’re trying to update it from otp 23 to otp 24.

your options are, keep at otp 23, or change your dependencies.