I'm tired of messaging my roommate about rent day

My roommate either disappears when the rent day comes or says, ‘I’ll send it as soon as my salary comes in,’ leaving me waiting for weeks. At first, I didn’t want to push too hard, but this month I had to borrow from my family. We have gone through this situation twice, and my patience is slowly wearing thin. What should I do in this case? How can I solve the problem without making it worse?