You can build up credit on Getaround, in particular through the referral programme.
This credit can be used when making a booking, either when you pay for the rental or when you select your excess reduction option. However, you can't use your credit to pay for an excess reduction option once you have made the booking.
Credit can be valid from a few days to a year depending on the reason of obtention. As an example, referral credits last for a year.
You have £40 credit and want to book a rental costing £30:
NB: credit in £ can only be spent on rentals with the same currency, ie in the UK. Likewise, credit in € cannot be spent on rentals paid in £.