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DecodeBase64 is Not Working For Me

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Posted on by Community Power Pla...

Hi all,

I am trying to build a flow that converts a Bearer token into a string I'm using the decodeBase64 method, but my Flows continue to fail at the step decodebase64 below is an error.

but the base64 string is get decoded on https://www.base64decode.org

Unable to process template language expressions in action 'Compose_3' inputs at line '0' and column '0': 'The template language function 'decodeBase64' was invoked with a parameter that is not valid. The value cannot be decoded from base64 representation.

Base64string is:

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

The concerned section of my flow looks like this:

Is there something wrong with my syntax?

please help!!

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Building flows

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Community Power Pla... on at

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@Chriddle, need your expert views on this.

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Community Power Pla... on at

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@v-yuazh-msft, need your expert views on this.

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Chriddle 8,443 Super User 2025 Season 2 on at

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Your base64 string is missing the padding (character[s] "=" added to make the last encoded block contain 4 characters)
Try this to add them (assuming your encoded string is in "Compose"):

decodeBase64( if( equals( mod(length(outputs('Compose')), 4), 1 ), concat( outputs('Compose'), '===' ), if( equals( mod(length(outputs('Compose')), 4), 2 ), concat( outputs('Compose'), '==' ), if( equals( mod(length(outputs('Compose')), 4), 3 ), concat( outputs('Compose'), '=' ), outputs('Compose') ) ) ) )

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Chriddle 8,443 Super User 2025 Season 2 on at

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The test for (mod 4 == 1) is superfluous, this cannot happen.

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KurtisRC 21 on at

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Thank you, I've been trying to work this out for 48 hours.
You are amazing, thank you sooooo much.

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