I'm a little curious, why does it take so long to list a coin on an exchange.
Do exchanges charge money from the developers or just a trading fee from the traders?
If a coin doesn't get listed in a very long time, will the project fail?
The more interesting a project will be the faster it can get into the list of an exchange. It also depends on the cooperation undertaken by the project developers and how the development prospects of the project in the market. Even to enter a classy exchange that requires a lot of supporting factors. Yes can be said at this time is not easy to enter an exchange.
But does it require them to pay a certain amount before they join?
The process are vary per exchanges. If a certain project shows strong and significant impact to the investors to the point that it causes hype within a not so long period of time, chances that it will land to exchange without any hassle requirements may be granted in no time.
Listing fees yes it has but even a project does have enough budget to fulfill the fees, it doesn't mean they will be listed right away at some of the popular and big exchange.
That's why for a start you can see tokens only landed on mid exchanges and sometimes not so popular while they are waiting for big exchanges to process their respective applications.
If the project will be failed if no listing happened? It depends if the development is continous and active.