Most common reason for approval is having correct documents and meeting the criteria.
For rejection
In my experience from viewing the group apart from not meeting requirements is people not filling out correct information in passport ( like special characters) using the autofill passport info and things not entering correctly. Take your time make sure everything is filled out correctly there is no refunds
Also refer to your embassy that you apply at , because it will be an equivalent in your local currency ( and the exchange fluctuates) so you will probably need a bit more then 500k to be safe