Without the copy of your passport (and residence permit, if you have a EU passport) we can not invoice the store for your VAT refund. The tax administration obliges us to store a copy of your passport (and if you have a EU passport, a copy of your residence permit) to prove that you are a non-EU resident and that you are eligible for a VAT refund.
At the moment, there is no structural collaboration between customs offices, businesses and the tax administration. Customs offices do not share the information they gather (passport and residence permit details) when they check your documents at the airport. Furthermore, customs officers can make mistakes. For these reasons, a customs stamp is not found sufficient by the tax administration, to prove your non-EU residency. Currently, a customs stamp is only considered as proof of the export of your goods. It is not found sufficient as proof that you are eligible for a VAT refund.
We are in debate with the tax authorities to strive for less requirements for our clients. We are pushing for more collaboration with customs offices. We hope that, in the future, we will no longer be required to archive a copy of your passport, and that taking note of passport and visa details will be sufficient. However, as long as the law is not changed, we need to follow the rules and regulations regarding VAT refund requests, to prevent retailers and ourselves from being fined due to an incomplete administration.
You can read about how to safely share a copy of your passport here.