Each learner enrolled in a course has session credits attached to their enrollment — this is what tracks how many sessions they've paid for, used, and have left. You'll typically see this broken down as something like Remaining, Consumed, and Total.
Credits move automatically as sessions happen: submitting your post-session feedback (see Submitting session feedback) is what deducts a credit based on the sessions-consumed value you enter. If a learner shows no credits assigned, that usually means their plan hasn't been set up yet on the admin side — worth flagging to your admin rather than trying to fix from your end.
Depending on how a course is configured or how billing is set up, you may not see a Remaining/Consumed/Total breakdown for every student — this is normal and doesn't necessarily mean something is wrong.