I would hesitate to recommend lower costs or similar as an incentive for people to use digital services as this can quickly become discriminatory. Further, in the case of Helsinki, mandatory services provided by the city must be equally accessible to everyone, whether or not they are able or willing to access them digitally.

Other incentives: faster (no need to physically go to the premises), more inclusive (for example, for people who don't have conventional schedules where they can go the their town hall from 9:00 to 17:00), real time update on the status of their demand...

Incentives can also be on the side of employees; it can be beneficial for them.

another incentive is the carbon efficiency, to be measured, of using a digital service instead of accessing it on premises

Needs to be clarified what is included in incentives.

i think this is tricky because it matters how cities approach this. I dont think we (can?) give financial incentives but i would look at the "gains" in a broader perspective. first time right, waiting times, speed