From the website:
A student's payment status is by the color of the credit card symbol located next to the student’s name at the top of the Messages thread. Open your Messages and locate the student's name. If the credit card icon is green, the student has payment information on file and you can proceed with scheduling lessons. If the card is yellow, then the student does not have payment information on file. Lessons should not be scheduled or held until the student puts payment on file with Wyzant.
You can also click Students & Lessons tab on the top of your page. From here, click Student Connections and you will see a list of all of your students. Payment status can be viewed here, as well.
From the app:
In the Wyzant app, select Students from your account dashboard. A student's payment status will be indicated by a colored dot located next to his or her name. A green dot indicates that the student has payment information on file. A yellow dot indicates the student has not added payment information.