In my case, im a single mother. No work. Its my boyfriend who invite me. He send invitation letter stating that he provide for all the lodging and boarding and also my airfareticket. And we state our main purpose to get to know each other because we are still in 3 years of relationship. Many seniors here said our letter is a red flag. We are red flag but we are being honest in our application. But look! I was approved. I also write cover letter. In my part i comply our remmittance since the begginning, my bank statement( 80kphp) my birth cert. my old pasport copies with stamp and refusals.my divorced cert( translated in english) my land title( under mortgage) my car or and cr, my childrens birth cert. and our emails and conversation in whatsapp and our photos together. Photos of our tavel outside the country and photos with my family. Btw, my travel history are in Japan( ex husband japanese and live for 5 years there) Hk, Macau and Thailand and i have 2 refusals before. France and Germany. And in my boyfriends part, he send me invitation letter, t4, bank statement and his company bank statement, birth cert. employment certificate his passport copy and income tax also his condo lease of agreement. And he send me a daily itenerary. We apply for 3 weeks. And my process takes 10 days before i got approved!
Hope it helps. And feel free to ask if you have some questions.