First, the interaction is not about the slopes themselves, but about thedifferencein the slopes. So, the test of the slopes is irrelevant.

Second, don't get too hung up on significance. The interaction would be valid even if it was not significant.

Third, I wouldn't report simple slope analysis at all. In fact, the presence of an interaction means that the simple slope analysis is invalid.

Finally, to examine theimportance(as opposed to the significance) of the interaction, I would calculate the predicted values of Y at various values of X and M.