If you have the correct Thinkific price plan ($79 per month or above) to issue completion certificates then Accredible and Thinkific are linked automatically and your certificates will be free to issue. Your Accredible account log in details are generated by Thinkific and these are the key to the automatic accounts integration.
To find your Accredible log in details follow these instructions:
1) Log into your Thinkific account
2) In the left hand menu select 'integrations'
3) Scroll down until you see Accredible. Here you will see your email and password that can be used to access your linked Accredible account.
4) head here: https://www.accredible.com/login and enter in those details
and you're in!
Here's a video that talks you through the process: https://www.youtube.com/watch?v=A6RkB_fBXPM