You can earn Free credits when you start using the app for the first time, but only available on selective plans when you subscribe for the first time.

At the time of writing this answer, Free Credit offered is as below:

➖ Yearly -   2000 Credits 

➖ Monthly - 700  Credits 

➖ Weekly -   100  Credits 

Generally, most users choose the Yearly plan as it also comes with 10 times more credits than the Weekly plan and costs just 32% of the Weekly plan for a year. However, the Monthly plan is still a better choice as it provides 4 times the credits and yet the subscription price is only 85% of the Weekly plan.