I read on the website here:
Purchase MANA with a credit card on Transak
Thanks to a new integration with Transak, you can now purchase MANA with a credit card directly from the accounts page by clicking the Buy button. Next, enter the amount of MANA you’d like to purchase in the widget along with your credit card information.
You can even purchase MANA to be deposited directly into your Polygon MANA account.
When I click buy over Polygon Mana I just see that its still ether on the Ethereum network.