Required triangles

Hello forum,
I have a fully tetrahedral mesh of a solid.
I would like to remesh it, but defining “as fixed” some triangles,
expecting that they are not affected by the remeshing process.
In particular, for my current case, the “fixed” triangles are not on the solid surface.
So I initialize the mesh using:

MMG3D_Set_vertex(mmgMesh,x_j,y_j,z_j,aRef,j); for all the nodes

MMG3D_Set_tetrahedron(mmgMesh,v1,v2,v3,v4,aRef,tetIndex); for all the tetrahedra

MMG3D_Set_triangle(mmgMesh,v1,v2,v2,aRef,trigIndex); for
=> for all the triangles of the mesh, also inner <= (not duplicated).

Then for all the triangles I would like to set as fixed:

MMG3D_Set_requiredTriangle(mmgMesh,index);

Is this set of API calls correct?
Grazie mille
Giovanni