Yes, you are welcome to begin a course in the audit track, then upgrade to the verified track soon after the course begins. Generally, you have until 10 days before the course ends to upgrade to a verified certificate. Some courses have an earlier payment deadline.
Note: You will not be able to upgrade to the verified track after the upgrade deadline has passed, or after the course has ended.
To find the specific deadline for your course, go to the course Home page, and then locate Verification Upgrade Deadline under Important Course Dates.
To upgrade, click the green Upgrade to Verified button under the course on your edX dashboard or the Upgrade to Verified Certificate link on the right side of the course's Home tab inside of the course.
Select the Checkout button to pay by credit or debit card or the Checkout with PayPal button.
If this is your first upgrade, you will need to successfully verify your identity on edX. ID verification involves taking 2 photos using a webcam, one of your face, and one of a photo ID card that has your name and photo on the same side. For tips on how to do this successfully, see Best Practices for edX Photo Verification.
You can check the status of your verification via your dashboard. Approval generally takes 2-3 business days. You can start working in your course while the approval is pending.
When you have a successful ID verification, it is valid for all edX courses for a year.