Issue a REFUND transaction for $310 and note in the description that you are depositing the excess into the trust account.  Write an Operating check for $310 and deposit it into the trust account and make a Payment to Account as you normally would for $$$ coming into the trust account. 

You will then have a zero A/R balance and a $310 trust balance that you can use to pay future charges.

Nancy Duhon, Esq.
Duhon Technology Solutions, LLC
Master Certified Consultant for Sage Timeslips
Providing individual Consultations and Third Party Remote Desktop Support - including older/unsupported versions.
404-325-9779
[email protected]

Thank you Nancy.

If you don't want it to show as having been received, you would need to virtually split the receipt into two portions.  For example, say the payment received was $1,000.00 on check #1234, you could enter it as Check #1234A for $690.00 into A/R and enter a separate Payment To Account into the trust account (Client Funds) for the balance of $310.00 using check #1234B.

Following up on Nancy's response, rather than a refund, you could also create a Transfer to Funds transaction to put the unapplied funds into trust.  This would be reflected as fully received on the bill.