underpaid due to basic salary, yes. but doesnt mean we're having no other income. i'll give u my own personal example:

i. publications

at the moment i'm not involved in any academic writings, but i was involved in publishing students' works and other faculty related jobs. as an assistant editor, i was paid about RM600-RM1.2k per job, which usually lasts between a week to 3 weeks. if i'm publishing my own work or book, then the pay is significantly higher, not including royalties i might get.

ii. consultations

as an architect, i still have to practice to maintain my knowledge in the industry. although i'm only involved in design stage (which truly not a hard thing to do), i'm paid between RM2.5k to RM4k per job. this freelancing jobs span between 3 weeks to 3 months. if i go part time, then the pay would be more consistent, around RM1.5k to RM2.5k per month. but if i practice as a full fledged architect part time, then the pay is about RM4k to RM6k per month.

iii. knowledge sharing

as academics we're often called to other educational institutions to give lecture or share our knowledge. at the moment the minimum pay for us is RM200 per hour. with a PhD it'll go higher, and ofcourse with a professorship, u can definitely demand alot. for example, i taught UTM's SPACE programme for 6 credit hours per week. that's easily RM1200, RM4800 per month.
there are other things also. like i said, the basic salary is low. but doesnt stop u to earn more