I have symmetrical mesh which I want to be used as tiles but as you can see on the picture there is a seam when I use the Array modifier is there a way to be made seamless?
The reason why your mesh doesn't tile well even though you make it symmetric with mirror modifiers is that mirroring only guarantees the vertices of mesh borders will meet, but it doesn't guarantee any smoothness of the resulting connection. You could do something like scaling the border down on Z axis with proportional editing enabled, or you can use a Smooth modifier. Also I recommend using Weld modifier instead of Mirror/Array merging. You can limit smoothing to a vertex group, though you should probably smooth that group if you need multiple iterations:
Also I just spotted you have some doubled vertices, select all vertices and press M, B.
Alternatively: tile manually, remove a connecting section and bridge edge loops with a smooth interpolation, then cut out again only the part that is supposed to tile and repeat your modifier stack: