I'd suspect nutrient deficiency. But they like higher pH. They also like a lot of nitrogen for growth although flowers and fruit can become aborted with too much.

I think you need a really large pot. I've only grown passion fruit outdoors, but the plants get huge and can easily take over a 20 foot long wall. Feeding might help a bit, but they really want to make a huge root system.

Thanks for the reply guys. I currently have the plant on the
window sill to maximize exposure to sun light. I keep trimming the plant to
keep it within the window frame. I will definitely get a bigger pot if/when I
move to a new apartment. I was really surprised that I could get the plant to
fruit in the first place. The growing season is short and not enough sun light.

I haven’t tested the soil for pH level. That is on the check
list for next growing season. I use a water soluble 18-18-21 fertilizer with micronutrientscouple of times in spring and fall. I didn’t want to over fertilize. Since I
was able to get buds and flowers, would that indicate that the amount of nitrogen is
sufficient?

The first "18" in your fertiliser is Nitrogen, the "21" is Potassium.
With the higher Potassium it does encourage more flowering. Higher
Nitrogen gives you more leaf and vine growth. Probably not a good idea
for indoors but Passionfruit likes poultry manure (aged). As it breaks down
it produces some Ammonia which raises the pH. As a kid I remember my
father used to grow a lot of it along the poultry run and we used to get
tonnes of fruit.

Do you know which kind it is? any pictures of the flowers and fruit from last year? I am in Southern Ont (near toronto) and had to add another plant(yellow edulis). The fact that you had fruit already is surprising. It could be cooler temp or lack of light. Usually soil should not affect it if it's local soil or potting mix.

I was able to get over a dozen fruit from my maypop passionflower in Ontario. Also grown in container. I set it out along a fence outside in the summer so it has space to grow. But the fruits had to ripen indoors (on the vine, which I kept in a south facing window) because they ran out of outdoor growing season. I grew them from cuttings, which can result in fruits sooner than plants from seed. Maypops are self-sterile, so I had a bluecrown passionflower to pollinate it. I have other species (edulis, tripartita, ligularis) which will begin their second season now, no fruits yet, but hopefully I'll get some in 2024, since they are a pretty good size and should hit the ground running this summer.