Check that the charge has a status of "Ready for Upload".
Check the budget tab of the job to see the Funding Type on the job. If the funding type is Recharge it should be billed. This is the most common reason that the charge does not get billed because the funding type is incorrectly marked.
If the funding type is State and it should be State check that the debit and credit for that charge have two different FAU's. Eg. material bought on a State job by Carpentry from Shop Stores should get charged as the Carpentry shop would get debited and Shop Stores would get the credit.