How to get additional prepaid shipping label? VFS New OCI card

With the prepaid shipping label I have already paid for, VFS sent one original document back (birth certificate). Now, they are asking to provide another prepaid shipping label. They gave the website . I am not understanding how to pay for additional prepaid shipping label through this website?

Independently, I want to go to fedex website and buy a shipping label from there. But, they are asking for a shipping address. In their FAQ it says that the printed shipping label valid only for 2 weeks. I don’t know when the OCI card will be ready by VFS to be mailed back to me. If I buy shipping label now itself, how to ensure its validity by the time they actually can ship it to me? (like it can be ready in a month or two or more, but shipping label i printed will be valid only for 2 weeks). Has any one faced this issue?