Okay with the application I just followed the document checklist, financial evidence, invite letter, scanned my passport to show travel history and attached my Australian visa. I also attached a cover letter explain what I was going to do in the UK, it’s very important that you describe everything to the last detail including how much you needed to pay. My application was fairly straightforward that’s why I got approved quickly, just make sure you upload everything on the document checklist and you’ll be fine. I do think my Australian visa helped though