Mandrill template merge fail - ruby

Question

I'm using mandrill to send emails from my API (in ruby with the mandrill-api gem), like signup confirmation email.
I have a merge tag in the template to put the username :
Hello *|USERNAME|*,
Thank you very much for installing the app! ...
...
My ruby code looks like that :
m = Mandrill::API.new ENV['MANDRILL_KEY']
template_name = "app-registration-welcome-email"
template_content = [{}]
message = {
:from_name=> "From Name",
:to=>[
{
:email => user.email,
:name => user.name,
}
],
:global_merge_vars => [{
:name => "username",
:content => user.name
}],
:merge_language => "mailchimp",
:merge => true,
:merge_vars => [{
:rcpt => user.email,
:vars => [{
:name => "username",
:content => user.name
}],
}],
:track_opens => true,
}
m.messages.send_template template_name, template_content, message
Unfortunately, when i receive the email, all is fine (to, name, from, ...) but the merge tag isn't replaced in the body and i still have *|USERNAME|* displayed.
What am I missing here?

Answer 1

You should only need to set USERNAME once, either in :global_merge_vars or :merge_vars.
If you're sending to just one recipient, it doesn't matter which you do.
If there are multiple recipients, use :merge_vars.
Try building message and then puts message.to_json and drop it into the debugger at https://mandrillapp.com/api/docs/messages.JSON.html#method=send-template (Click the 'Try it' button.) See if that gives you any clues.
You might also try using "USERNAME" instead of "username" as your variable name. The docs say merge vars are case-insensitive, but it's worth removing one more possible mismatch.