"Failure to post to Librato" error

[spachari-im]

In my project we post metrics to Librato with the instance Id and cluster name as source.
For some cloud VMs, I see the following error and then there are no subsequent Metrics reported.

The error in the log is :
2021-06-14 23:36:06.094 ERROR com.librato.metrics.reporter.LibratoReporter Failure to post to Librato: code:400 response:{"errors":{"params":{"source":["CLUSTER_NAME is not a valid source name"]}},"request_time":1623713765}

I have truncated the actual CLUSTER_NAME in the log above, but it is a string of 257 chars. The same metric works for instances where the CLUSTER_NAME is up to 256 chars.

I am guessing this is due to the character limit, but can this be confirmed in the error message? Also, it would be good if the logs showed the metric for which the source attribute has this error.