For this there would be no particular OpenVPN functionality, so you would need to extend it beyond that. There are seemingly unlimited paths that you could choose for this, though few (if any) are going to already be laid out and ready without requiring you to develop a solution. One example of how this could be done is by using FreeRADIUS for OpenVPN authentication, and then having billing software which provisioned FreeRADIUS authentication.
In this example, you can see how to set OpenVPN to use FreeRADIUS here:
Then you can see here there is an old (perhaps in need of updating) plugin for WHMCS (popular billing software) to manage FreeRADIUS accounts:
As far as I know a clean end-to-end solution does not exist for this, but I hope that I have given you some ideas of how you can begin to proceed with such a task.