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 orange, then the student does not have payment information on file.
Once a tutor replies, students must add billing information to their accounts before continuing to send messages. Lessons should not be scheduled or held until the student puts payment information on file with Wyzant.
You can also check their account status from your Student Connections page.
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.