I submitted my application through Linkedin. FDM got into contact with me and arranged both rounds of interviews within a few days. The HR team is very approachable and understanding, and the whole process was very smooth.
As others have mentioned, the phone interview focuses mainly on my understanding of FDM and my motivation to join as a software developer. It was not stressful and there was not difficult questions.
The second+third round of interview (conducted within the same day) focuses more on the technical side. The second interview consists of an aptitude test (1 hour), a logic/ Venn diagram test (1 hour), and a math test (15 minutes). For people with a STEM background, all tests should be quite manageable, although there are some questions on basic software development/ programming concepts that may be unfamiliar.
The third interview is with the FDM regional head. I think it will depend largely on the personality of the interviewer. My experience was that it is better to be honest about what you don't know, and talk about concrete examples that show your motivation to learn and your interest in an IT/ finance career. My interviewer was very sharp and knows the area very well, and did not hesitate to ask difficult questions when I gave ambiguous answers about my experience in IT/ finance.