Capistrano Rails deploy - authentication error - ruby-on-rails

Question

I'm trying to deploy a Rails app onto a Digital Ocean Ruby on Rails droplet. I thought it would be all set up to go and I'd just have to configure the app. But it's actually just like a standard Linux server.
I'm using this guide to set up the droplet, but had to tweak a few things to get them running. When I run cap production deploy, I get the following error message:
#<Thread:0x0000555b2f0ec948#/home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/runners/parallel.rb:10 run> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
12: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/runners/parallel.rb:12:in `block (2 levels) in execute'
11: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/abstract.rb:31:in `run'
10: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/abstract.rb:31:in `instance_exec'
9: from /home/michael/.rvm/gems/ruby-2.6.5/gems/capistrano-passenger-0.2.0/lib/capistrano/tasks/passenger.cap:42:in `block (3 levels) in <top (required)>'
8: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/abstract.rb:61:in `test'
7: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/abstract.rb:148:in `create_command_and_execute'
6: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/abstract.rb:148:in `tap'
5: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/abstract.rb:148:in `block in create_command_and_execute'
4: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/netssh.rb:130:in `execute_command'
3: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/netssh.rb:177:in `with_ssh'
2: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/connection_pool.rb:63:in `with'
1: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/backends/connection_pool.rb:63:in `call'
/home/michael/.rvm/gems/ruby-2.6.5/gems/net-ssh-6.1.0/lib/net/ssh.rb:268:in `start': Authentication failed for user michael#178.128.223.202 (Net::SSH::AuthenticationFailed)
1: from /home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/runners/parallel.rb:11:in `block (2 levels) in execute'
/home/michael/.rvm/gems/ruby-2.6.5/gems/sshkit-1.21.0/lib/sshkit/runners/parallel.rb:15:in `rescue in block (2 levels) in execute': Exception while executing as michael#178.128.223.202: Authentication failed for user michael#178.128.223.202 (SSHKit::Runner::ExecuteError)
(Backtrace restricted to imported tasks)
cap aborted!
SSHKit::Runner::ExecuteError: Exception while executing as michael#178.128.223.202: Authentication failed for user michael#178.128.223.202
Caused by:
Net::SSH::AuthenticationFailed: Authentication failed for user michael#178.128.223.202
Tasks: TOP => rvm:hook => passenger:rvm:hook => passenger:test_which_passenger
(See full trace by running task with --trace)
Here is my deploy.rb file:
# config valid for current version and patch releases of Capistrano
lock "~> 3.14.1"
set :application, "MyApp"
set :repo_url, "git#github.com:MyAccount/MyApp.git"
# Default deploy_to directory is /var/www/my_app_name
set :deploy_to, "/home/michael/my-app/#{fetch :application}"
# Default value for linked_dirs is []
append :linked_dirs, "log", "tmp/pids", "tmp/cache", "tmp/sockets", "public/system", "public/uploads", "vendor/bundle", ".bundle"
# Default value for keep_releases is 5
set :keep_releases, 5
And the deploy/production.rb file:
server "123.456.789.123", user: "me", roles: %w{app db web}
set :ssh_options, {
config: false,
keys: %w[/home/myhome/.ssh/id_ed25519],
forward_agent: true,
auth_methods: %w[publickey],
user: 'me'
}
Any help here would be good. All the other answers I've seen so far haven't fixed the problem for me (and none have had Tasks: TOP => rvm:hook => passenger:rvm:hook => passenger:test_which_passenger)