If you are out of credits, or want to buy credits for the first time, there are two easy ways to do so.
Order on the website
Head to the Rolla Dashboard
Select the "Buy Credits" tab on the lefthand menu
Follow the prompts to select your package and pay!
Order via the Rolla app
Create a new project.
Complete filming the project so you reach 100%.
When you proceed to checkout, you will see a prompt that alerts you that you are out of credits. Tap the "Get credits" button.
Follow the prompts to select your package and pay!