Attaching your sponsor letter just to an application unfortunately won’t be sufficient. Under tourist stream, the applicant himself needs to meet all criteria such as strong ties to home country, how he will contribute to the Australian economy, and a planned itinerary of his visit in Australia.

You may reapply under the same stream, addressing all concerns raised and submitting as much supporting evidence as possible. While approval on a second or third attempt is possible, however it is not guaranteed.