How to add subscriptions without generating new invoice

Hello, I hope you all are doing great.

I want to add subscriptions without generating new invoice. Suppose if i have a user who took 1 subscription plan at 10th of particular month and billing cycle is 20th of every month , and now he took 1 more subscription plan after 6 days that is on 16th, so how would i bill his both subscription plans in same invoice.

Kindly help me.

I am still facing same issue , suggest solution.