How do I search by attribute in DynamoDB? I inherited a site that uses DynamoDB for its database, which I know nothing about unfortunately, and I'm trying to change a user's email for them.  There appears to be a users table in DynamoDB, but I don't know the user's id, only their username and current email, so at this point, I am just trying to find the record before updating it.  When I attempt to scan for these values in the web interface, I get no results; it just keeps searching.  If I scan in the web interface for an email address which I know exists, I also get no results.
Using these placeholder values,
Username: example
Email: example@example.com

I have tried a few commands using AWS CLI, but I get various errors:
aws dynamodb get-item --table-name users --key '{&quot;Username&quot;: {&quot;S&quot;: &quot;example&quot;}}'

This yields this error:
Unknown options: example}}', {S:

I have also tried this:
aws dynamodb query --table-name users --key-condition-expression &quot;Username = :v1&quot; --expression-attribute-values &quot;{ \&quot;:v1\&quot; : { \&quot;S\&quot; : \&quot;example\&quot; } }&quot;

This yields this error:
An error occurred (ValidationException) when calling the Query operation: Query condition missed key schema element: id

I have also tried printing out all users, but it appears to fail for anything but the smallest tables:
aws dynamodb scan --table-name users

This yields this error:
An error occurred (ProvisionedThroughputExceededException) when calling the Scan operation (reached max retries: 2): The level of configured provisioned throughput for the table was exceeded. Consider increasing your provisioning level with the UpdateTable API.

Not sure what to do at this point.  Any advice?
I contacted AWS support, and they said two things:

The read/write capacity of the table needed to be changed from &quot;provisioned&quot; to &quot;on-demand&quot;.

Scan is definitely the command to use here, not query; query requires the id, scan does not.
aws dynamodb scan --table-name users --filter-expression &quot;Username = :v1&quot; 
    --expression-attribute-values &quot;{ \&quot;:v1\&quot; : { \&quot;S\&quot; : \&quot;example\&quot; } }&quot;