How to best handle imbalanced text classification with Keras?
First of all, to reassure you, SMOTE should work on text data. SMOTE will work on any data type as long as there is a way to compute the distance between data points.

Based on the error message you receive, it seems that it's an implementation issue (adding part of your code or how much data you have would greatly help).

As the error states, you have only 3 samples but the method requires at least 6. My guess is that something went wrong and you should have much more than 3 samples.