The process is okay, but very long. From what I know, if I were able to get an offer, I would need to go through 7 rounds:

1. HR (culture fit, why Adyen, why move to the Netherlands)
2. Two engineers (why Adyen, tell me about a project you are most proud of)
3. Codility test (easy level)
4. Interview with two engineers to discuss the Codility test (prepare for the details of the Codility test, why you did that in that way, what can be improved (time complexity and space complexity), why Adyen). I failed here. Reasons are unknown.
5. Interview with the technical manager (I did not proceed to this round)
6. Interview with prospective colleagues (I did not proceed to this round)
7. Interview with one member of the management board (I did not proceed to this round)

In general, I do not have too many complaints about the process. It is just that I got rejected for unclear reasons and asked for feedback but never got a reply.

1. Why Adyen?
2. Why did you move here?
3. What motivates you?
4. What is the project you are most proud of?
5. How do you optimize a slow SQL query?
6. What are the differences between Left Join, Right Join, Inner Join, and Outer Join?