They are very confused what is their requirements and they were looking for frontend developer but later after 3rd interview they said they want a full stack developer. They should not waste time for candidates who they don't think matching their skillset.

I submitted an application for the role on LinkedIn and subsequently received a call from the HR, who scheduled a assessment to take place one week later. The assessment consisted of two components: a coding challenge on the Hackerrank platform, which required me to merge anagrams, and multiple-choice questions (10 in total) related to the job description I had applied for. Following a 30-minute wait, I participated in a face-to-face interview with the hiring manager, which focused primarily on behavioral and situational questions rather than technical ones. The interview itself lasted 30 minutes and included queries about my motivations for applying to Amgen and relevant past experiences.