private void checkIfCanAddAmountForCompleteEnrolmentModel(final Money amountToAdd, final Event event, final DateTime when) {
if (hasAlreadyPayedAnyAmount(event, when)) {
final Money totalFinalAmount = event.getPayedAmount().add(amountToAdd);
if (!(totalFinalAmount.greaterOrEqualThan(calculateTotalAmountToPay(event, when)) || totalFinalAmount
.equals(getPartialPaymentAmount(event, when)))) {
throw new DomainExceptionWithLabelFormatter(
"error.accounting.postingRules.gratuity.SpecializationDegreeGratuityPR.amount.being.payed.must.be.equal.to.amout.in.debt",
event.getDescriptionForEntryType(getEntryType()));
}