Trouble configuring "google/cloud/ai_platform/v1" gem (Ruby)

[wwa]

I'm trying to access Vertex AI using ruby "google/cloud/ai_platform/v1" gem.
Minimal reproducer:

require 'google/cloud/ai_platform/v1'
::Google:‌‌:AIPlatform::V1::DatasetService::Client.configure do |config|
  config.credentials = "/home/user/promptest/test/prvkey.json"
end

The file contains correct service account key. Code fails with:

Traceback (most recent call last):
        4: from chat.rb:10:in `<main>'
        3: from /var/lib/gems/2.7.0/gems/google-cloud-ai_platform-v1-0.35.0/lib/google/cloud/ai_platform/v1/dataset_service/client.rb:71:in `configure'
        2: from chat.rb:11:in `block in <main>'
        1: from /var/lib/gems/2.7.0/gems/gapic-common-0.21.1/lib/gapic/config.rb:84:in `block in create_setter'
/var/lib/gems/2.7.0/gems/google-cloud-ai_platform-v1-0.35.0/lib/google/cloud/ai_platform/v1/dataset_service/client.rb:2087:in `block in <class:Configuration>': uninitialized constant GRPC::Core::Channel (NameError)

Searching for this error does not seem to yield anything useful. Please help.