Photoadking looks OK at first sight - it's a freemium model - don't buy anything until you've checked it out. Canva is the market leader so check that out as well. In my experience the issue isn't the software so much as the design idea, so check out their templates. If you're not sure what you want you could always hire someone with good reviews on Fiverr for a few bucks and see what they come up with.

Don't reinvent the wheel: check out your competition. What's working for them? (eg is your marketplace like sideprojectors.com or flippa.com? These are two very successful sites: is there a good reason NOT to use their business models?)

Let's have a chat about it if you'd like to discuss further.

Lots of ideas in the answers here, and maybe one question to answer is: what do my competitors do? Because there are very few questions that are totally new and I'm a believer in not reinventing wheels unnecessarily.
Another principle to apply, in my view, is simplicity. I think many folks are tired of complex pricing models. Bear in mind that transactional pricing can become quite complicated if you have to track those transactions (and potentially police them if your clients are tempted to cheat).
So I'd be tending towards simple pricing - perhaps with a freemium model that sucks your customers in, gets the directory going, builds a client base and track record quickly.

Happy to talk it through if you wish.

Try asking yourself - where does my target customer hang out? If your product is targeting professional business people, then LinkedIn would be a good place to start. But if your customers are consumers and predominantly female aged 14 - 25, perhaps TikTok would be better. Older consumers of both sexes are more likely to be on Facebook, so that's also a good place. If you want to sell to elderly consumers, there may be no best place!
Let me know if you'd like to chat further.

As others have pointed out, this question can be answered in many different ways. Perhaps before diving into the endless possibilities, it's worth asking yourself a few questions:
a) Why do I want to make money online? Is it because the more conventional methods of making money are not open to you, or are you perhaps thinking this is going to be easier? (It's not an easy way to make money, by the way.)
b) What am I enthused by? If you still want to make money online, then the best way to stick at something that is going to suck out your energy is to do something you enjoy. What interests you? What are you knowledgeable about?
c) Where can I find buyers for whatever I have to offer? In other words, do I know where there's a market? The answer may be linked to the previous question. For example, if you're a gamer and a member of a gaming community, then you will know how to access that community. They could become your first customers.

Taking this approach will be a more fruitful way forward than making random choices which are less likely to succeed. Happy to talk this over if you wish.