EPW calculation regarding 2D Material

[kazirafakathossain]

For EPW calculation of 2D materials it's told that it can be made possible by treating it as a 3D one by including vacuum. My question is what should be the minimum value in angstrom along z-axis for succesfull calculation. I've used the following parameters but still getting error during calculation for 2D hexagonal InN :
celldm(1) = 6.859706 [a=3.63]
celldm(3) = 5.509642[c=20]
Should 'celldm(3) / c' be greater than celldm(1) for succesful treatment like a 3D structure and is any other change required in the code or any inclusion of any parameter in the code?