Reimbursement, interest

(1) Insofar as an administrative act has been withdrawn or revoked with effect for the past, or has become ineffective as a result of the occurrence of a resolutory condition, benefits already rendered must be reimbursed. The benefit to be reimbursed is to be fixed by written administrative act.
(2) For the extent of the reimbursement, with the exception of interest, the provisions of the Civil Code on the surrender of unjust enrichment apply correspondingly. The beneficiary may not invoke the lapse of the enrichment insofar as he or she knew of the circumstances leading to the withdrawal, the revocation or the ineffectiveness of the administrative act, or did not know of them as a result of gross negligence.
(3) The amount to be reimbursed bears interest, from the point in time the administrative act becomes ineffective, at five percentage points above the base rate per annum. Recourse to the interest claim may in particular be dispensed with where the beneficiary is not responsible for the circumstances leading to the withdrawal, the revocation or the ineffectiveness of the administrative act, and renders the amount to be reimbursed within the period fixed by the authority.
(4) Where a benefit is not used for the determined purpose soon after payment, interest under subsection (3), first sentence may be demanded for the time until it is used for that purpose. The same applies insofar as a benefit is drawn on although other funds must be used proportionately or in priority. Section 49(3), first sentence, no. 1 remains unaffected.