Remix an existing audio sample (a sound effect, ambiance, or music clip) into a variation guided by a text prompt, for example turning a track into an 80s synthwave or metal version. Both the sample and the prompt are required; the sample is uploaded as a URL or base64 audio and must be at most 15MB or the call returns HTTP 400, and duration must be one of the allowed values (0 means match the source, otherwise multiples of 10 up to 180 seconds). Synchronous: the call blocks until generation finishes and returns a single audio result containing a URL; there is no separate polling step. The optional modification_strength (0 to 1, default 0.5) controls how far the result departs from the original. Credits are charged on success. Use this to transform existing audio you already have; use createSoundEffect, createAmbiance, or createMusic to generate audio from scratch. Pass an optional request_id to tag the result so you can locate it later via getAudioResults. Requires an API key (user scope).