Can I manually give a guest credit?

Yes, you can add an amount to a guest's credit yourself in your overview, for example as compensation after an outage, as a welcome gesture, or for family who should not have to pay. The guest sees no difference from self-purchased credit and can use it in the same way. In your own overview it remains visible what is purchased and what is credited credit. It is intended as an incidental gesture, not as a structural discount or solution for an excessively high kWh price or unreliable measurement.