Why is my Samsung a31 vibration not working

@zinabutenna fierst you want to make sure that it is set to work in your settings. DO a reset on your software and see if that resolves it.

If that does not fix it, follow the Samsung Flowchart

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.