How to declare a integer-valued matrix?

My data is a matrix X with the dimension 100 \times 3, whose each element follows a Poisson distribution. Therefore, each element of it must be nonnegative. I wonder how I can declare such matrix in the data block? because an error message reminds me of defining X correctly.

You can define a 2D array of non-negative integers like:

int<lower=0> X[100, 3];

Does this solve your error? If not what was the message?