Not able to creacte mirror internal

[elektro_freakz]

I am new to forms and i'm following a youtube tutorial how to replicate a dashboard part with a 3d scan. But i am stuck at the moment.

The instructions say that i have to use symmetry mirror - internal to create some kind of mirror line using 2 faces. But everything i try i get the same message:

Could not determine the symmetry from the selections. Continue selecting edges and vertices, master side followed by mirror side.

Could not determine the symmetry from the selections. Do both sides have the same number of faces?

When i use the function on a sphere created by fusion it works without a problem. So i guess its model specific problem.

What am i doing wrong?

[elektro_freakz · Accepted solution]

Can be closed. Found the solution to my problem..
Should have listened to fusion, i made sure both sides, left and right of the mirror line have the same amount of faces and the symmetry is roughly how it should be. 

 

[TrippyLighting]

I often look at other users' designs, and one thing I recommend is to decide which side of the mesh you like and then delete the other. Then, use mirror/duplicate.