Hi here, @sharp75. Thanks for your question.
We have several types of Prepaid Rate Plans so it really depends. On most of our Prepaid Rate Plans, if you finish your included data, your data will just cut off. You'll then have to recharge again for more data by doing a standard recharge or purchasing a Data Add On.
Automatic Data Top Ups after exceeding your data inclusions is currently only on our Postpaid plans.
I recommend looking for the Prepaid Rate Plan you're on in our CIS page to get an idea on how your Prepaid Rate Plan works.
If you're unsure what rate plan you're on, you can text "BAL" to "9999" (this is a free SMS) and you'll get an SMS from us advising the name of your plan and your remaining credit.
Alternatively, you can also check the My Optus App under "Service" and you'll see the name of your plan there.
Hope this helps! Let us know if you have any other questions. 🙂