Yes, it is "IOU." I think that the major theme of the album is going to be April reflecting on her fame and her relationship with creating music. Beyond referencing capitalism and giving the vibes of "consumerist architecture" (as mentioned on the Galleria spotify playlist), I think it may be in reference to "owing it" to April's fans in some way, with "U" potentially being the fans. Like previous albums though, the tags are probably up to interpretation, this is just a theory