How to get rid of seam after rejoining objects

I have a mesh that I had to separate the top lip from in order to weight paint correctly. After rejoining and plugging the model into the game, the lip separates at points when the character speaks, right where i previously separated it. Is there any method to get rid of this seam? I don’t have an unsplit ver of the mesh, as I transferred weights from another model, and didn’t save beforehand.

You said re-joined… but did you merged by distance ?

I didn’t think about that, I just used ctrl J. I’ll try it out, Thanks!

Thanks That did it!