Unknown validator: 'URLValidator' (ArgumentError)

I’m trying to set up forest admin on my Rails app.

On the step
rails g forest_liana:install abcd

I get the following error message in terminal:
/Users/—/.rvm/gems/ruby-2.6.6/gems/activemodel- `rescue in block in validates’: Unknown validator: ‘URLValidator’ (ArgumentError)

My gemfile

ruby ‘2.6.6’
gem ‘pg’, ‘>= 0.18’, ‘< 2.0’
gem ‘puma’, ‘~> 3.11’
gem ‘rails’, ‘~> 6.0.4’, ‘>=’

Hello @oddb ! :wave: Welcome to our community :tada: :confetti_ball:

I have never encounter this issue.

Can you try to run bundle install in your rails app first ?
Also, can you share your entire Gemfile ?

Thanks in advance