Learnerships

Hi, Can someone please advise as to how the payments of a learnership should work? Example when running a learnership you start of with example 7 learners so you invoice the client for 7 learners as the contact sessions continue learners drop out so you adjust your invoice according to the number of learners left? is this correct?  Than you find yourself in a situation where there is one contact session left meaning the learner completed 99% of the qualification and drop out, should you invoice for that learner or not?

Need some feedback please as the contact between the provider and the client is not very clear on this