The following points are one of the primary reasons that impact Cost Per Conversion.

1. Optimization: Your ad should be well optimized like, use informative content in you ad, use relevent keywords, landing page should be redirected correctly.

2. Audience: You can run the perfect campaign for the perfect product (your event) but it won’t convert unless it reaches the right people. So targetting the correct audience is one of the most important factor which effects the CPA.

3. Landing Page: Your landing page could be the problem, you’ve done everything perfectly so far. Great product, great ad but if the landing page of the ad is not correct or relevent all your efforts will become zero.

4.  The Thing which you want to promote: It could have eye-catching imagery, convincing copy and a slick landing page. But none of that matters if the final product sucks.

Through CPA you get charged for your ads and you pay only for the action a person chooses to take on stumbling upon your ad. You can choose the actions to pay for like Page likes, link clicks, showing interest/disinterest, etc.

The following factors can work wonders for your Facebook campaign:

• Data Insight: The ad campaign must be designed by taking targeted audience in consideration. See to it that whether your campaign will reach people who don’t know about it but have a relevant interest.
   
• Landing Page: A landing page is highly necessary for any campaign on Facebook, be it an ad campaign or one like your musical event. Create a simple yet impressive landing page where users are able to retrieve information easily.
   
• Imagery: Make your ad campaign successful by using catchy images and videos which will lure people to click on it.
   
• Placement of campaign: It is to be kept in mind that the campaign should reach to a larger audience. Hence, the appropriate placement of the should not be taken lightly so that the campaign is made visible to more and more people.
   

So, if your basic requirements for reaching out to a larger audience is fulfilled and above steps are followed diligently then your CPA is bound to increase with time. This is due to the fact that the number of people coming across and reacting to your ad campaign will be increasing with each passing day.

I agree with Pankaj that for good CPA, it's very important that your ads are well optimized for the right audience. If your ad campaign has been designed after taking in consideration what kind of audience is the most likely to click on them, your CPA is bound to increase much more than your expectations. Always make sure that the links for your site's landing pages are working flawlessly. Quality of ads, whether videos or images, play a very important role in making an ad campaign successful. One must try getting insight into the latest ads trends to figure out what kind of content catches the maximum eyeballs.

I hope this answer serves the purpose.

Hi

According to Facebook, Cost Per Action (CPA) is a way of getting charged for your ads that allows you to pay only for actions a person takes because they saw your ad. The actions you can choose to pay for are Page likes, offer claims, mobile app installs or link clicks.

There are some factors that affect your CPA without any change in campaign:

Audience :

The audience you choose directly affect how much you are paying for facebook ads. By creating a high quality ad, you will be able to stand out among your competition when you are trying to bid for an ad. Audience is an important part of the cost and sharing the information to the right audience helps in increase of CPA.

Quality :

The quality of your ad can send the cost higher to lower. The quality directly affects the cost of ads. Quality Score is a calculation of how relevant your ads, keywords, and landing page are to a person seeing your ad. Having a high Quality Score means your ad, keyword, and landing page are all relevant and useful to someone looking at your ad.

Campaign Appearance :

The appearance of your campaign and it’s usability factors affects your CPA. Using optimized keywords and phrases related to the topic of the campaign which is part of the paid inclusion can make the cost per action more effective.

Competition:

The higher the demand for campaign is the more you may need to pay in order to appear in top ad positions in Google. This affects your CPA as you need to spend more to gain a click.