Jekyll + Netlify trouble running netlify functions

I’m new to Netlify and I’m trying to set it up with a Jekyll site to do some API calls.
So far I’ve added

functions = "_functions"

to the netlify.toml file, created the _functions folder with a js file inside just running some simple testing code:

exports.handler = async function(event, context) {
    return {
        statusCode: 200,
        body: JSON.stringify({message: "Hello World"})
    };
}

netlify-cli is installed, and also ran netlify link and linked it to the netlify site.
Then I’m confused what to do, I tried running netlify dev but I get the following jekyll error:

bundler: failed to load command: jekyll (/usr/local/bin/jekyll)
/Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/spec_set.rb:89:in `block in materialize': Could not find concurrent-ruby-1.1.9 in any of the sources (Bundler::GemNotFound)
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/spec_set.rb:82:in `map!'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/spec_set.rb:82:in `materialize'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/definition.rb:185:in `specs'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/definition.rb:255:in `specs_for'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/definition.rb:237:in `requested_specs'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/runtime.rb:91:in `block in definition_method'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/runtime.rb:20:in `setup'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler.rb:148:in `setup'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/setup.rb:20:in `block in <top (required)>'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/ui/shell.rb:136:in `with_level'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/ui/shell.rb:88:in `silence'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/setup.rb:20:in `<top (required)>'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/cli/exec.rb:61:in `require_relative'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/cli/exec.rb:61:in `kernel_load'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/cli/exec.rb:28:in `run'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/cli.rb:494:in `exec'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/cli.rb:30:in `dispatch'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/cli.rb:24:in `start'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/exe/bundle:49:in `block in <top (required)>'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/lib/bundler/friendly_errors.rb:130:in `with_friendly_errors'
        from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.15/exe/bundle:37:in `<top (required)>'
        from /usr/local/bin/bundle:23:in `load'
        from /usr/local/bin/bundle:23:in `<main>'
◈ Command failed with exit code 1: bundle exec jekyll serve -w. Shutting down Netlify Dev server

And I also tried netlify functions:invoke and I get an
Error: Ran into an error invoking your function: request to http://localhost:8888/.netlify/functions/geo-api failed, reason: connect ECONNREFUSED 127.0.0.1:8888

To be honest, I’m not sure what I’m doing at this point, but if anyone can help it would be appreciated.

This simply appears to be a problem about missing a gem. You might want to install it.