The importance of UX is widely recognized by product developers among automotive OEMs. A distinctive UX shaping the brand is an important goal in the development of a new product generation. Trends such as advancing digitalization and connectivity of products open up numerous innovation potentials for UX developers. This contribution focuses on in-vehicle UX in terms of designing interactions between the vehicle and the user. In academia, theories and models to explain the phenomenon of user experience are widespread. Furthermore, numerous research approaches in the field of engineering sciences pursue the goal of making user experience measurable and evaluable. However, in the course of our literature review, we found that there is currently a lack of tools and methods that support product developers in eliciting user needs and subsequently synthesizing concepts. For this purpose, particularly the early phase of product development offers required creative freedom. However, this phase is also characterized by a high degree of uncertainty. These circumstances raise the question of which challenges product developers face when designing interactions. This paper aims to contribute to this question through a two-step descriptive analysis in cooperation with a leading German automotive group. Based on a literature review, challenges and strategic potentials were first discussed with UX experts in a workshop (n=11). From these results, a total of 28 hypotheses were derived, which were then evaluated in a second step in an online survey (n=45) by a broad set of experts. Subsequently, the challenges identified in this way were translated into four qualitative success factors to provide product developers with concrete recommendations for action. Additionally, a total of seven requirements were extracted from these factors to help product development research close the identified research gap in further prescriptive studies.