must i pay for recordbox 7

No, you don't need to pay to use Rekordbox 7 in Export Mode. Or with the basic features in Performance Mode. 

When using Performance mode but not a hardware device that is officially supported you will be limited to the features that you can use.
If you have a hardware device that is connected or registered as owner registration it will make more features available but not all. 

tl;dr No you don't need to pay to use Rekordbox 7. You have only gotten a free trial of a subscription plan that will not auto renew.