libclntsh.so.19.1: cannot open shared object file: No such file or directory

[saslani]

I am using Ruby / sinatra and I am using oracle 12c:

I am getting the following error in heroku logs:

LoadError: libclntsh.so.19.1: cannot open shared object file: No such file or directory - /tmp/build_d670f82963726e051daafee73cc48e98/vendor/bundle/ruby/2.6.0/gems/ruby-oci8-2.2.7/lib/oci8lib_260.so

1. any idea what could cause this?
2. why is it looking for version 19.1, shouldn't it be 12.x?

my gemfile:

ruby "2.6.4"

gem "activerecord-oracle_enhanced-adapter", "5.2.6"
gem "puma"
gem "rake", "~> 12.3"
gem "ruby-oci8", "2.2.7"
gem "sinatra"
gem "sinatra-activerecord", "2.0.13"

-----> Detecting rake tasks
       Could not detect rake tasks
       ensure you can run `$ bundle exec rake -P` against your app
       and using the production group of your Gemfile.
       rake aborted!
       LoadError: libclntsh.so.19.1: cannot open shared object file: No such file or directory - /tmp/build_d670f82963726e051daafee73cc48e98/vendor/bundle/ruby/2.6.0/gems/ruby-oci8-2.2.7/lib/oci8lib_260.so