How can I pay a subscription fee for Apple's account developer mobile application?

You can log in to the following link

https://developer.apple.com/programs/enroll/

then click at Start Your Enrollment icon at the bottom of the end page and then follow the rest of the steps,

Note: Before paying, you must have the DUNS number, In case of account type, individuals do not need to extract DUNS number

The following images are for clarification