Looking at the code the former is valid. What you are getting is invalid syntax error but because it is missing parentheses in the code and ruby will think that `{` is starting a block. Could you change that to use the parentheses?

```irb
>> def foo(a, b)
>>   p a
>>   p b
>>   end
=> nil
>> foo {action: "post"}, {multipart: true}
SyntaxError: (irb):5: syntax error, unexpected ':', expecting '}'
foo {action: "post"}, {multipart: true}
            ^
(irb):5: syntax error, unexpected ',', expecting $end
foo {action: "post"}, {multipart: true}
                     ^
	from /opt/boxen/rbenv/versions/1.9.3/bin/irb:12:in `<main>'
>> foo({action: "post"}, {multipart: true})
{:action=>"post"}
{:multipart=>true}
=> {:multipart=>true}
```