我的孩子也是今年申请. 请进来:

https://appsupport.commonapp.org/applicantsupport/s/article/How-do-I-assign-my-recommenders

your son needs to Invite & Assign his counselor first.   By doing so,  his counselor will receive an email invitation,  then his counselor is able to upload the Recommendation Letter.        

Counselor can upload the Letter before your son completes/ submits his application.