Yes I am. I’m not on ACF Pro, however (so I’m working with the limitations of ACF 4. Sorry for not mentioning that sooner.). So if I use
'return' => '%post_url%',
Then I get brought to this url: http://mydomain.com/%post_url%?post_id=127
Which loads up as:
Bad request!
Your browser (or proxy) sent a request that this server could not understand.
Error 400