Which systems can you connect?

Any two with documented APIs you have access to, such as Stripe, Twilio, SendGrid, HubSpot, Pipedrive, Airtable, Google Sheets or your own backend.

Who pays for hosting?

It runs in your own cloud account, so you pay its hosting directly. Small integrations usually fit in the free or lowest tiers, but that depends on your volume.

Can you move our old records too?

Bulk migration of historical records is outside this offer and quoted separately.

Is there any support after the revision round?

14 days of written fixes for defects in the delivered scope. Anything beyond that is Ongoing maintenance.

Who switches from test credentials to live, and when?

You switch, after your own test run, with written instructions in the README. App369 can do it in a scheduled session if you prefer.

Do I need a call before I pay?

No. The scope, price and delivery time are on this page, and everything happens in writing. If you want to talk live, calls cost $100 per 15 minutes, paid upfront.

Who owns what you deliver?

You do. The code, videos and files delivered under this offer belong to you once paid.

Fixed-price offerConnect two systems through their APIs, at a fixed price

Someone on your team copies data from one tool to another every day, or a no-code zap breaks without telling anyone. The two systems are connected directly through their APIs, with retries, logs and tests, and deployed to your own cloud account.

Pay $1,200 & start

Full refund if Simon can’t take it on once he sees your project, or if you cancel before work starts.

Check fit by email

Simon does the work himself
5.0 from 127 Fiverr reviews, checked Oct 30, 2026
Paid to App369 LLC through Stripe. Receipt by email, invoice with your company name on request.

$1,200 fixed price, 5 business days after API docs and test credentials for both systems arrive.

Price checked October 25, 2026.

No call needed. Ask a question first by email at contact@app369.com or with the contact form; we reply by email, usually within one business day.

API Integration

Two systems that should talk to each other but don’t. For example, a won deal in your CRM creates a Stripe invoice, or a new lead sends a Twilio text. Built with retries, logs and tests, so it keeps working.

$1,200

fixed price, 5 business days

You get

One integration between two systems with documented APIs, covering up to 3 event types
Triggered by webhook or on a schedule
Retries with backoff, and checks so nothing is created twice
Logs, plus an email alert when a sync fails
Automated tests against mocked APIs
Deployed to your cloud account (Cloud Run, Cloud Functions, Cloudflare Workers or Vercel), with a README
One revision round

Not included

Systems without an API, or API access you don’t have
Bulk migration of historical records
User interface work

Delivery

5 business days after API docs and test credentials for both systems arrive.

Simon built and runs Workspace369’s Stripe, Twilio and SendGrid integrations.

Pay $1,200 & start

Full refund if Simon can’t take it on once he sees your project, or if you cancel before work starts.

After you pay

Simon emails you within one business day to confirm and send the access checklist. You can also send it straight away to contact@app369.com. What the work needs:

The two systems and what should happen when (for example: a deal is won, so an invoice is created)
API docs for both systems
Test credentials for both, and which cloud to deploy to

Delivery takes 5 business days after the test credentials arrive.

Full refund if Simon can’t take it on once he sees your project, or if you cancel before work starts.

Not sure it fits? See who it fits, or email a question about this offer; we reply by email, usually within one business day.

This fits when

Won deals are retyped as invoices by hand
New leads should trigger a text, an email or a task straight away
A Zapier or Make flow fails silently or has grown expensive
Two systems disagree and nobody knows which one is right

Errors this fixes

Each page explains the error from the vendor’s own docs, with what to try first.

How it works

Pay and describe the flow
Name the two systems and what should happen when, then send API docs and test credentials for both.
Build the sync
Webhook-triggered or scheduled, covering up to 3 event types, with retries and checks so nothing is created twice.
Test
Automated tests against mocked APIs, then a run against your test accounts.
Deploy and hand over
Deployed to your Cloud Run, Cloud Functions, Cloudflare Workers or Vercel account, with logs, an email alert on failure and a README.

What the handover notes look like

An example of the handover notes every integration in this offer ships with: when a deal is marked won in a CRM, a draft invoice is created in Stripe for someone to review and send.

Event	What happens	If it arrives twice	If it fails
Deal marked won	Finds or creates the customer in Stripe, then creates a draft invoice with the deal’s line items	The deal ID is saved on the invoice, so a second delivery finds it and stops	Retried with a growing wait; after the last try, an email alert with a link to the deal
Deal amount changed	Updates the draft invoice while it is still a draft	Nothing changes when the amount already matches	Retried, then an email alert; an invoice already sent is left alone, and the alert says so
Invoice paid in Stripe	Marks the deal paid in the CRM	Stripe event IDs are logged and repeats are skipped	The endpoint returns an error so Stripe retries (up to three days in live mode); an email alert follows if it keeps failing

Deal marked won
What happens
Finds or creates the customer in Stripe, then creates a draft invoice with the deal’s line items
If it arrives twice
The deal ID is saved on the invoice, so a second delivery finds it and stops
If it fails
Retried with a growing wait; after the last try, an email alert with a link to the deal
Deal amount changed
What happens
Updates the draft invoice while it is still a draft
If it arrives twice
Nothing changes when the amount already matches
If it fails
Retried, then an email alert; an invoice already sent is left alone, and the alert says so
Invoice paid in Stripe
What happens
Marks the deal paid in the CRM
If it arrives twice
Stripe event IDs are logged and repeats are skipped
If it fails
The endpoint returns an error so Stripe retries (up to three days in live mode); an email alert follows if it keeps failing

Sample only: an example flow, not a client’s systems. A real build names your two systems, covers up to 3 event types and is tested against mocked APIs, then against your test accounts.

Read Stripe’s webhook delivery rules

Built before

Work Simon has shipped that uses the same kind of build. Every project links to something you can check.

2023–nowOur own product

Workspace369

SaaS, iOS & web

An all-in-one workspace for service businesses: CRM, proposals, invoicing and payments, scheduling and a shared email, SMS and voice inbox. Designed, built and run by App369.

Flutter app on iOS and the web, live on the App Store
Firebase backend split into 20+ Cloud Functions codebases
Stripe billing, Twilio voice and SMS, inbound email security

FlutterFirebaseTypeScriptStripeTwilio

Case study App Store

2026Open source by Simon Dziak

Scrape to Dashboard

Data pipeline

A polite crawler feeding a validated SQLite ETL with price history, published as a static dashboard and CSV export. Demonstrated on a public scraping sandbox.

TypeScriptSQLite

GitHub

Questions before you pay

Which systems can you connect?: Any two with documented APIs you have access to, such as Stripe, Twilio, SendGrid, HubSpot, Pipedrive, Airtable, Google Sheets or your own backend.
Who pays for hosting?: It runs in your own cloud account, so you pay its hosting directly. Small integrations usually fit in the free or lowest tiers, but that depends on your volume.
Can you move our old records too?: Bulk migration of historical records is outside this offer and quoted separately.
Is there any support after the revision round?: 14 days of written fixes for defects in the delivered scope. Anything beyond that is Ongoing maintenance.
Who switches from test credentials to live, and when?: You switch, after your own test run, with written instructions in the README. App369 can do it in a scheduled session if you prefer.
Do I need a call before I pay?: No. The scope, price and delivery time are on this page, and everything happens in writing. If you want to talk live, calls cost $100 per 15 minutes, paid upfront.
Who owns what you deliver?: You do. The code, videos and files delivered under this offer belong to you once paid.

Fiverr reviews / 95 on app work

What buyers said about this kind of work

Read 126 of the 127 reviews

“Outstanding work! He went above and beyond to make an amazing app for me! I will definitely be working with Szymon again!”
Mark, United States, April 2021. App development on Fiverr
“I work with Szymkn to fix bugs and implement small features and he always delivers on time. thanks again”
A buyer in the United States, January 2021. App development on Fiverr
“This seller did an amazing job again. He always knows exactly how to complete any crazy ideas I bring to him. Thank you”
A buyer in the United States, December 2020. App development on Fiverr

Read the whole story

Sixteen five-star reviews from one buyer: mobile apps, app design and a Shopify store (Mark, United States)
A large custom app build, delivered on the back end and the front end (A buyer in the United States)

Ready to start?

Pay online and send what the work needs by replying to the Stripe receipt. Simon, who builds and runs the SaaS Workspace369, does the work himself.

Pay $1,200 & start

Full refund if Simon can’t take it on once he sees your project, or if you cancel before work starts.

Related fixed-price offers

Fixed scope, fixed price, paid upfront. The work happens in writing; no call needed.

Looking for something else? See all fixed-price offers

Fixed-price offerConnect two systems through their APIs, at a fixed price

API Integration

You get

Not included

Delivery

After you pay

This fits when

Errors this fixes

How it works

Pay and describe the flow

Build the sync

Test

Deploy and hand over

What the handover notes look like

Built before

Workspace369

Scrape to Dashboard

Questions before you pay

What buyers said about this kind of work

Read the whole story

Ready to start?

Further reading

Related fixed-price offers