Hi @HPB,
Thanks for sharing your question with the Community! Love to see users taking advantage of segmentation tools to deliver a targeted flow.
You can create a segment that will target these users who have purchased Product A only once with the rule "Ordered Product equals A Once overall times". Unfortunately, there is no way to exclude people who purchase product A along with other products.
If you are creating a segment-triggered Flow, it should be noted that users will be pushed through the flow only when they are added to the segment. If you create the segment first, then create the flow, you will need to back-populate the flow to push through users who were already pulled dynamically into the segment.
Additionally, for more insight into how segment-triggered flow work, I’d recommend checking out this post made by a fellow user!
Thanks for your participation in the Community!
-Taylor