Power Query , try other

Hi,
Can some expliain why one of these works and one does not, so this works ;

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but this does not ?

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as far as i can see the otherwise is outside to the List.Accumulate ? do I just need the try elsewhere or is there some point I'm missing as to why this does not work. I'm not looking for alternatives just explaination as to why 'sum' works and 'accer' does not.

Thanks, will do.

I did try otherwise within but it still did not work ? is this what you meant ?

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But i did find an if statement works ;

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thanks for the help, sorry can't give a rep, I might have a lambda question so if someone else responds I'll be able to again.