You want to know if you can file a negative return with TrustFile.
It is not possible to file negative returns in TrustFile as they are not accepted by the state. If you need to file a negative return or receive a credit from the state, you will need to reach out to the state directly to see if they will issue the credit to you.
If you are unsure why credits from refunded transactions are not being included on a return in TrustFile, more likely than not the amount of the refunded transactions would have created a negative amount within the jurisdiction they are aligned to and thus could not be added to the return. They will be saved until the sales for the jurisdiction surpass the amount of the credit. The credit will then be applied on the return.