I have problems on how to manage payments. The entry fee is € 190.00 that can be paid or all or a deposit of 80.00 €. How do I know who I still have to pay? Thank you.
Partial payment from the front end is not yet available in CiviCRM, but it can be done through the extension described in this CiviCON presentation "Front End Partial payments"
It's avaialble in Github.
Your use case is similar to this situation: What will be the way to give user public access to check their contribution?