Hi there, mushahidlatif.
It's a pleasure to have you join us here in the Community. I'm by no means an accounting professional, but I do have some insight to provide that can help get you on the right track to recording this.
In the situation you've explained, you could enter these entries as billable expenses. With this, you'll be to use the right account when you enter a bill/check (expense) for the registration and when you invoice (income) them as the service provider.
To show you how this works in QuickBooks, allow me to walk you through the steps on how to create a billable expense:
Once the expense transaction has been created, here's how we can invoice the customer:
Just a heads up, this method can impact your books and you may wish to seek additional guidance from an accounting professional. Every business is unique and they can make suggestions on how to handle this. If you're not affiliated with one, then our Intuit Find-A-ProAdvisor site can help you to find certified professionals in your area.
That should do it! I'm confident that with these resources you'll be able to enter billable expenses like a pro in no time.
You're always in good hands here in the Community. If you need more help with your expenses please don't hesitate to reach out to me again. Wishing you a lovely day.