DEV Community: Mohsindev369

A webhook retry can pay a customer twice, and two checks that stop it

Mohsindev369 — Fri, 30 Oct 2026 00:38:30 +0000

If you sell credits or usage through Stripe, LemonSqueezy or Polar, your webhook handler will receive the same event more than once. Providers retry when your server is slow, when a deploy lands mid-request, when a response gets lost. If the handler does balance += 100 every time it sees checkout.session.completed, somebody eventually gets paid twice.

The fix is two checks, not one. Here is what each one does and why the second exists.

Check 1: de-dupe on the event id, inside the same transaction

Keep a table of events you have handled, keyed by provider and event id. Insert before you do any work, and skip the work if the insert did nothing:

await db.transaction(async (tx) => {
  const inserted = await tx
    .insert(billingWebhookEvents)
    .values({ provider, eventId, type: eventType })
    .onConflictDoNothing()
    .returning({ eventId: billingWebhookEvents.eventId });

  if (inserted.length === 0) return; // a retry of an event we already handled

  // ...do the actual work with tx
});

The primary key is (provider, event_id). The detail that matters is the transaction. If the work throws, the de-dupe row rolls back with it, so the provider's next retry is processed instead of being swallowed as already handled. The common version of this bug checks first and processes after, and a delivery that failed halfway is then lost for good.

Check 2: a unique constraint on the thing being paid for

Event ids are the provider's idea of uniqueness, not yours. One checkout can in principle reach you under two different event ids, and once several billing providers sit behind one interface you can't rule it out. So the purchase itself gets a unique key, and you insert it before the balance moves:

const [purchase] = await tx
  .insert(creditPurchases)
  .values({ teamId, provider, providerCheckoutId, credits })
  .onConflictDoNothing()
  .returning({ id: creditPurchases.id });

if (!purchase) return; // this checkout already paid out

If the row already exists, the credits were granted for this checkout, whatever event id carried it. Check 1 protects you from redelivery. Check 2 protects you from your own assumptions about the provider.

Make the increment atomic

The last piece is easy to miss. Do the increment in SQL, not in JavaScript:

await tx
  .insert(credits)
  .values({ teamId, balance: packCredits })
  .onConflictDoUpdate({ target: credits.teamId, set: { balance: sql`${credits.balance} + ${packCredits}` } });

balance + N runs inside the database, so two concurrent deliveries for the same team can't read the same starting balance and overwrite each other. A read, add, write sequence in application code can.

Test it against a real Postgres

This is the part that earned its keep. Mocks agree with whatever you wrote, because a mock doesn't enforce a unique constraint or roll back a transaction. A real Postgres does both. The tests that matter deliver the same event twice and the same checkout under two different event ids, then assert the balance moved once:

no-ops a redelivery of the exact same event id
doesn't double-grant when the same checkout is delivered under two different event ids

When I added tests like these against a real database, they caught two real bugs in my own billing code that I had read past more than once.

What to copy

If you only take one thing from this: put the de-dupe row and the work in one transaction, and give the paid thing its own unique key. Everything else follows from those two.

This is the pattern in Keel, the Next.js SaaS starter I'm building and selling. The webhook handler, the credit grant and the tests are all in the repo, and there is a demo with no sign-up if you want to see the product around it.

Tip for freelancers and Clients going to hire freelancers

Mohsindev369 — Wed, 17 Jan 2024 19:52:37 +0000

Having a good order brief makes ALL the difference!

For all web design clients looking for freelancers, please do yourself (and your chosen freelancer) a favor by creating a clear and concise order brief.

It helps us understand your vision, budget, timeline, and specific needs. This leads to:

✅ Better communication: Less back-and-forth, more focused collaboration.
✅ Fewer revisions: Reduced risk of missed expectations and rework.
✅ Smoother project flow: Everything runs smoothly from start to finish.

If I were your freelancer I would need the following in your order brief

Project Overview:

✅ Project Name:
✅ Company Name:
✅ Website URL (if applicable):
✅ Project Description: Briefly summarize your project goals and desired outcomes.

Target Audience:

✅ Who are you trying to reach with your website?
✅ What are their needs and expectations?

Functionality Requirements:

✅ What features and functionality do you need on your website?
✅ Are there any specific integrations or plugins you require?

Design Preferences:

✅ Do you have any specific design styles or references in mind?

// Side Note: let the designer make colors, fonts, and overall aesthetic decisions don't micro-manage if he's the expert Let him cook.

Budget and Timeline:

✅ What is your estimated budget for this project?
✅ What is your desired timeline for completion?

Content: ✅ Do you have any existing content that can be used? ✅ What additional content needs to be created?

Bonus:
Include any relevant examples of websites you like for inspiration.
Remember: The more detailed your order brief, the better equipped your freelancer will be to deliver a website that exceeds your expectations.
Let's make web design projects a success for everyone!

hashtag#webdesign hashtag#freelancer hashtag#orderbrief hashtag#projectmanagement hashtag#tips

🎯 Overcoming Impostor Syndrome in the World of Web Development 💻

Mohsindev369 — Fri, 25 Aug 2023 19:10:39 +0000

Hey There 👋

Today, I wanted to talk about something that many of us in the web development community have likely experienced at some point in our careers: Impostor Syndrome. 🤔

Impostor Syndrome is that nagging feeling of self-doubt and inadequacy, even in the face of accomplishments and evidence of competence. It's that voice in our heads that whispers, "Do I really belong here?" or "Am I just lucky, or do I actually know what I'm doing?" Trust me, you're not alone if you've ever had these thoughts. 🙋‍♂️🙋‍♀️

In the fast-paced and ever-evolving world of web development, it's easy to feel like you're falling behind or that you're not as skilled as your peers. But here's the truth: You've come a long way, and you deserve to be where you are! 🚀

Here are a few strategies I've found helpful in combating Impostor

Acknowledge Your Achievements:

Take a moment to reflect on your journey. Remember the projects you've successfully delivered, the complex code you've tackled, and the problems you've solved. These accomplishments are proof of your skills and dedication.

Embrace Continuous Learning:

Web development is all about growth. Instead of fixating on what you don't know, focus on what you're learning. Every challenge you overcome adds to your expertise.

Talk About It: Don't be afraid to open up to your colleagues or mentors about how you're feeling. You'll likely find that they've experienced similar thoughts and can provide valuable perspective.

Celebrate Progress:

Break down your larger goals into smaller milestones. Celebrate each achievement along the way. It's a great way to remind yourself of your capabilities.

Remember You're Not Alone:

Impostor Syndrome is more common than you think. Many successful developers have dealt with it too. It's a sign that you care about your work and want to do your best.

Practice Self-Compassion:

Treat yourself with kindness. Remember that making mistakes is a natural part of learning and growing. Don't be too hard on yourself.

Let's turn Impostor Syndrome into Impostor Strength! 🦸‍♂️🦸‍♀️ Remember, every challenge you face and overcome is a step forward in your journey. You belong in this field, and your unique skills contribute to the vibrant web development community.

Have you experienced Impostor Syndrome? How do you overcome it? Let's start a conversation and support each other in the comments below! 👇

Get network information using JavaScript and optimize your app

Mohsindev369 — Fri, 21 Apr 2023 22:33:32 +0000

Have you every wanted to optimize your web application behavior based on the user internet performance? Maybe loading content in different qualities?

Network Information API

This API is accessed through the navigator.connection property. Here are some of the properties.

effectiveType
downlink
errt
saveData

effectiveType
The effectiveType property returns the effective type of the current connection.

navigator.connection.effectiveType //'slow-2g','2g','3g','4g'

downlink
The downlink property returns the effective bandwidth.

navigator.connection.downlink //Bandwidth in mbps

rrt
rrt property returns the round-trip time.

navigator.connection.rrt //round-trip time (ms)

saveData
The saveData property returns a Boolean, Weather the user's data-saver is on or off.

navigator.connection.saveData //true or false

Using it in a practice example

Less say we want to represent a high quality video, We first make sure that data-saver is not enabled. And if the internet speed meets their requirements, We load the video accordingly.

if(
!navigator.connection.saveData &&
navigator.connection.effectiveType === '4g' &&
navigator.connection.downlink>2
) 
{
 loadVideo("4k")
} else {
loadVideo("low-quality")
}

Thanks for reading. This I my first blog so sorry if there is any errors.