Thank you again for answering my question. Finally, the error was that the data matrix obtained from an MNE RawArray has a transposed shape, inversely to how it should be implemented in the MEEGtoolkit function. To solve it, it was enough to transpose the data using two alternatives depending on the library we use: data.T (with numpy) or data.transpose (with pandas).
I hope this can be helpful to someone who has encountered the same problem.