If you joined OSPS before 1 October 2017 you are in the DB section.
If you joined OSPS after 1 October 2017 you should look at the Investment Builder page as the rest of this page is not relevant to you.
Members of the DB section can transfer benefits into Investment Builder. These benefits can be combined with their DB section benefits as part of a maximum cash calculation at retirement, but none of the transferred funds can be used to purchase additional pension in the DB section.
You can pay in more than your normal contributions if you wish. These are called Additional Voluntary Contributions or AVCs. If you want to pay AVCs to OSPS the only option is to pay them into Investment Builder.