There seems to be a syntax error in your code:
class exposure(ref="0") sex (ref="0") age(ref="0") id //param=ref; /* you have 2 slashes */
Also, you say you have only binary variables, but AGE_2CLASS is not listed on the CLASS statement. Either use AGE on the model statement or put AGE_2CLASS on the CLASS statement?
model outcome=exposure sex exposure*sex age_2class /dist=poisson link=log;
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