The rated charge of the usage is too low to be billed (and Unbillable Rules are configured to SPIN this unbillable code).
Common Resolution(s)
Actions you can take to resolve the problem:
This may be configured to SPIN just to provide visibility. In this case this record can be left alone (it will eventually age and no longer be visible) - or it can be purged immediately if desired.
If the usage record should be billed anyway, choose Override Rule on the usage record. If this is done frequently, consider a change to Unbillable Rules for this Unbillable Code.
Details
This usage has been rated and the charge to be billed is very low. The unbillable rule configuration specified a threshold value and action that caused it to SPIN.