DPhil program Interview at University of Oxford-Experince

Oxford University DPhil interview experience:
Yesterday, I attended the final interview for my DPhil program. Three months ago, my supervisor interviewed me and was convinced that we had developed a strong research proposal together. Following his advice, I submitted the proposal, and I was later invited for a second and final interview.
The interview was held on Microsoft Teams and included seven professors. As per the graduate office guidelines, I presented three slides. During the Q&A, one professor asked me to define and provide the formula for a specific technique I had included in my presentation. While I clearly explained the concept, he pressed further for the exact formula.
Since the research proposal focuses on work to be developed during the PhD, I didn’t have the formula at this stage. I couldn’t provide it, which I now worry might impact my chances. However, I handled the rest of the questions well.
What’s concerning is that my supervisor, who was present but silent throughout the interview, contributed significantly to the research proposal and is highly interested in working with me. If my application is rejected, his efforts might also be undermined.
How likely will I receive an offer, considering my supervisor’s support and the collaborative effort on the proposal? Does not knowing the formula during the interview significantly harm my chances?