Numma Factura Fácil
Validating a $12K/month business idea with a $2,000 experiment
The Challenge: Mexican businesses wait 7 days for invoices, losing payment cycles and cash flow.
My Approach: Smoke test with fake landing page + targeted ads to validate demand before building.
The Surprise: We targeted entrepreneurs. Accountants responded 3x more, changing our entire business model.
Timeline 4 months
Role Research & Conversation Design
The Impact (TL;DR)
FIRST CUSTOMER
Accountant managing 25 client invoices
3x HIGHER RESPONSE
Accountants vs Entrepreneurs
FIRST CUSTOMER
Accountant managing
25 client invoices
What I Validated
Real willingness to pay ($2,900-12,500/month from accountants)
Better business model: B2B2C (1 accountant = 50 clients) vs B2C individuals
Product-market fit exists—but for a different customer than we assumed
Key Learning
Being wrong about your customer early is better than being right too late. Our pivot from entrepreneurs to accountants unlocked 10x better unit economics.
The Problem
Day 4-5
Desperate follow-ups
Multiple channels, client angry
Day 4-5
Desperate follow-ups
Multiple channels, client angry
Day 4-5
Desperate follow-ups
Multiple channels, client angry
Day 2-3
Waiting in silence
No visibility or updates
Day 1
Request sent via WhatsApp
Message lost among 50+ others
The 7-Day Invoice Nightmare
7 days lost per invoice = 1 missed payment cycle
30-day cash flow impact for small businesses
Dozens of times per month for 67% of businesses
In Mexico, 67% of small businesses create invoices by:
1
WhatsApp message to accountant → Lost among 50+ daily messages
2
Wait 2-3 days in silence → No visibility, client getting angry
3
Multiple follow-ups → *Emails, calls, more WhatsApp
4
Accountant manually processes → 4 different systems, 20,000 tax codes
5
Invoice arrives on day 7 → Payment delayed 30 days
Why this complexity?
Mexican SAT (tax authority) requires specific fields, formats, and codes for compliance. Even accountants find it tedious—creating a massive automation opportunity.
The Bet
Business Idea
Hypothesize
Test
Experiment
Learn
What if businesses could invoice directly through WhatsApp the app they already use all day?
My hypothesis: Mexican entrepreneurs would pay for autonomy. AI handles SAT complexity. Users just describe what they need in natural language.
Before building anything, I designed an experiment to test if people would actually pay for this
The Experiment
Experiment Components:
Landing page with clear value proposition
A/B testing: Entrepreneurs vs Accountants
Lead qualification system via ManyChat
Meta Ads + Google Ads targeting
Validating Demand with a Smoke Test
Goal: Not just measure clicks, talk to real people facing this problem daily.
I launched a fake product: a landing page promising complete Numma service (which didn't exist yet) + paid ads.
Week 1 Results
29,925
impressions
$1,920
MXN Spend
654
Clicks
10
Leads
10
Interviews
$2.94
CPC
The Numbers Validated Demand—But the Insights Changed Everything
Quantitative validation:
$2.94 cost per click = strong interest
10 qualified leads willing to do 30-min interviews = real pain
Qualitative surprise
Accountants responded 3x more than entrepreneurs
They wanted this tool for their clients, not for themselves
Key quote: "It's not about autonomy. It's about speed."
This insight redirected the entire product strategy.
From assumptions to insights
Research Methodology:
The experiment validated demand, but not the why behind it. Using ethnographic interviews combined with Service Design methodology, I conducted 30-minute structured conversations with the leads generated from the campaign.
Who I Talked To:
5 entrepreneurs
(freelancers to small business owners)
3 accountants
(managing 5-25 clients each)
2 early adopters
(ready to pay before MVP existed)
10 Interviews Revealed What Ads Couldn't
I conducted 30-minute conversations with all 10 leads to understand the why behind their interest.
ENTREPRENEUR
I don't care who does it, as long as it's fast and I can get paid.
ACCOUNTANT
My clients message me at 11pm for invoices. I'd love to give them self-service for simple ones.
EARLY ADOPTER
If this works, I'm paying immediately. I lose clients because I can't invoice fast enough.
The Pivot
INITIAL HYPOTHESIS
RESEARCH REALITY
Target
Entrepreneurs seeking independence
Accountants wanting to scale
Pain
My accountant is slow
I can't grow without hiring
Value
Do it yourself
Clients self-serve, you supervise
Pricing
$350-500/month
$2,900-8,300/month
Model
B2C (acquire 100 individuals)
B2B2C (1 accountant = 50 users)
Why This Mattered:
Better unit economics: 1 accountant manages 10-50 clients = better LTVHigher willingness to pay: Business tool to scale practice, not personal expense
Validated by behavior: First customer (Carlos, accountant with 25 users) came via referral
From Insights to Design
Differentiated Messaging for Different Needs
Same visual structure. Completely different copy and pricing.
For Accountants:
Headline: "Multiply your practice without hiring"
Pricing: $2,900-12,500/month (10-100 client RFCs)
Message: Automation + supervision
For Entrepreneurs:
67 leads from 5,749 visits
Accountant page: 1.53% conversion (3x better than generic 0.67%)
First paying customer: accountant managing 25 invoices
Data source: Your analytics June-October 2025
Interested in how I design products?
Let’s Collaborate
carlos@cabras.co
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