Thanks for opening this issue; this is actually a poor error message that I will fix.

The issue with this program is you are using assume in the wrong place. The PAY_EXPR of a parallelReduce is evaluated in a pure context, where assume is not allowed because it could introduce a failure.

This issue can be fixed by moving the assume(amount > 0, "EZERO"); into the PUBLISH_EXPR. For example,

const axferParams = declassify(interact.getAxfer());
// assume ....
// return ...

I will update the corresponding documentation to mention this restriction.

A couple other things worth pointing out in this program:

1. You'll need to specify a paySpec branch in order to pay with non-network tokens in parallelReduce
2. And update the values of the parallelReduce's PAY_EXPR to be in pay amount format.

Both are documented here: https://docs.reach.sh/ref-programs-step.html#%28tech._pay._amount%29

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Thank you

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