Unable to batch enroll batch of 20+ students

I’m running a Tutor instance of open edx. At the moment, batch enrollment can only be run with up to 8 emails. Running with 20+ emails yields “Error enrolling/unenrolling users”. I followed the instruction here: https://help.appsembler.com/article/11-enrolling-learners

In Network tab, students_update_enrollment got: 502 Bad Gateway nginx.

Can someone support me on batch enrolling a large number of students? Thank you.