How would you go about validating the need for an app to split the bill when people go out to restaurants or bars?

Before we begin the answer, let's put a structure in place that can help us think through things in a logical and coherent manner>

Structure:
1. Clarifying questions
2. Users
3. lay out the thought process on how to approach this. - this should cover pre-development activities, During development activities and post Development activities
4. Measures of success

Clarifying questions:
1. Is this going to be an app that is entering a brand new market or are there other competitors already? - Assume that there are other competitors
2. Who is going to build this app? Google ? is this going to be a new feature offering? - Assume yes -
3. What is the goal here for us? - Customer acquisition and adoption
4. Assuming that this would only be for the US market and we do not have to worry about supporting multiple currencies etc? - Sure
5. Does this app need to only show the split for the bill or do we need to allow for transfers and payments as well? - Account for transfers etc.
6. Are there any constraints that I need to know about? - assume that you have all the information needed for this.

Users:
1.  Customers who go out to restaurants and bars with friends/family or acquaintences
2. Banks and credit card companies
3. local business establishments?
4. 3P payment providers (stripe, paypal, Amazon pay etc.)

We can focus our efforts on targeting the first set of users above as they are going to be the primary group.

Now that we know what the scope is and who the users are, let's focus on what we will do to know if we ned an app or not.
We will split this into pre-development, development and post development activities:

1. Pre-development activities:
a. Market analysis and competitor intelligence - Here, I will do a comprehensive study on the market to understand the need for an app. I will look at who the current players on the market are and do a SWOT analysis.
b. Gaps and user requirements - I will also undertake an extensive cusotmer survey either on our own or partnering with a survey company to understand user sentiment and needs. I will try and gain an insight into what customers feel the current apps lack and what they would want from the app.
c. Define vision, USP and monetization opportunities - Once we have the data that we need, I will begin driving a vision plan to understand what we need to build and how this will create a USP for our app that would give us a competitive advantage in the market.
Here, I will also work on brand messaging that will help define the app and its usefulness to customers.
As part of this, I will also identify montization opportunities (such as paid app vs taking a percentage cut for transactions vs freemium model etc.)

2. Developmen activities:
a. work with engineering teams to build app and ensure that we the right features prioritized for our customers.
b. partnerships with payment providers is other set of work that we will need to conduct.

3. Post Development activities:
a. Beta Rollout and testing - here, I would conduct A/B tests on various UI solutions when rolling out the product to a limited set of customers and collect feedback and iterate.
b. Full rollout -

Measures of success:
North Star metrics:
# app downloads
# frequency of use (DAU/WAU/MAU etc.)
# of transactions or 'bill splits'
# avg total value of transactions.

Secondary metrics:
#NPS
# total revenue generated
# Financial transactions in the app as a % of total bill splits
 

P.S: I have intentionally kept some sections light here as I could not type anymore (long day at wok.. lol) - But I hope to have gotten the thought process correct.

Thigns I could have expanded on:
1. security of transactions
2. barriers to entry etc.