Invalid base64 Error when invoking Lambda - AWS CLI [Fixed]

Borislav Hadzhiev

Last updated: Feb 26, 2024
2 min


# Invalid base64 Error when invoking Lambda - AWS CLI

The "Invalid base64: {"key": "value"}" error most often occurs when a Lambda function is invoked with --payload parameter consisting of JSON without setting the --cli-binary-format to raw-in-base64-out.

Invalid base64 error

To solve the error, set the --cli-binary-format parameter to raw-in-base64-out when invoking the Lambda function.

aws lambda invoke --function-name testFunction --cli-binary-format raw-in-base64-out --payload '{"name": "John Smith"}' response.json

with raw input

If you are on Windows, you have to escape the double quotes in the --payload parameter - '{\"name\": \"John Smith\"}'.

The reason the AWS CLI throws the error is that by default the --payload parameter is of type blob and expects valid base64 encoded input - docs.

By setting the --cli-binary-format parameter to raw-in-base64-out we are able to provide a raw JSON string to the --payload parameter.

Note that the --cli-binary-format parameter has to be set toraw-in-base64-out, even when passing a file to the --payload parameter.

For example, if we had an event.json file with the following contents.

{ "name": "John Doe" }

Then you have to invoke the lambda function as follows.

aws lambda invoke --function-name testFunction --cli-binary-format raw-in-base64-out --payload file://event.json response.json

invoke with param and file

If we were to not set the --cli-binary-format parameter we would still get the "Invalid base64" error.

with file without param

I've also written detailed guides on how to invoke a Lambda function using AWS CLI and how to create a lambda function with AWS CLI.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

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