Visible lines on your Normal map are not necessarily an indication of an error. A normal map records the direction that faces are orientated and since these have to be laid out on a flat UV space it also needs to take that into account, so if two adjacent pieces of a mesh ( where you have a seam ) happen to be orientated in different directions on your UV map then the normals will seem to be disjointed, but that’s because they may be upside down in relaion to each other on the UV map so the normals ‘flip’ their direction to compensate for that.
Here’s a sphere that has one single seam running around the equator, the ‘bumpiness’ is a baked Normal map from a Displacement on a hi-res model.
On the left this is the Normal map in the Normal channel with a simple colour [ it looks fine], In the Middle is the exact same sphere but I’ve put the Normal map into the Base Colour Channel … and the seam is obvious. On the Right is the Normal map in BOTH the Base colour and Normal channel. You can see the seam … but the ‘bumpiness’ is still correct.
Looking at the Normals Map for this sphere;
You can see that there is no way the seams could be aligned, so the Normals are baked to accurately account for the layout on the UVmap.
Try rendering you character with the Normal map only in the Normal channel and the rest of the texture set up as you desire, and it should look fine.