Service marketplace connecting clients with advisors and business experts for online consultations, built on Mercur

Montelink is a Polish marketplace that connects clients with independent advisors and business experts, who showcase their qualifications on their profiles, for online consultations – with per-minute pricing shown before booking, no waiting rooms, and no bureaucracy.

The catalogue of services offered by experts spans a wide range of business support areas and dozens of categories, with its scope expanding every day. These areas include legal, tax, accounting, audit, HR, global mobility, and IT and digital transformation services.

For consultants, Montelink is a one-stop shop: a single place to serve clients, manage their services online, and build brand awareness – no separate booking tool, payment provider, or marketing funnel required. Advisors pay a recurring subscription for platform access, and Montelink takes a 5% transaction fee on every order.

A consultation is not a product with a fixed price. What it costs depends on how long the session runs, and standard eCommerce checkout logic has no way to handle that. Montelink needed booking, billing, and video delivery to work as a single flow, on a platform where the sellers are independent professionals.

Billing by the minute

Every commerce platform assumes a product has a price attached to it before checkout. A consultation provided by an independent expert through Montelink only has a final price once it ends. A client buys a block of time up front, and the session may run past it.

That meant tracking session duration in real time, comparing it against the pre-purchased block, and charging the difference automatically once the meeting closes. None of that exists in a standard checkout, and none of it can be approximated with fixed-price products or manual invoicing at marketplace volume.

Splitting payments between the platform and independent experts

The experts selling on Montelink are independent professionals, not a merchant network. Money paid by a client has to reach the right expert, without every advisor setting up and managing their own payment infrastructure.

EU tax rules apply on top. Consultations sold across borders are subject to EU VAT rules that differ for business and consumer clients, so the applicable rate has to be determined per transaction. Getting the split right and the tax calculation right are two separate problems, and both had to be automatic.

Availability that matches each expert's calendar

Experts run their consulting practice outside Montelink as well as on it. A slot that looks free on the platform is worthless if the expert is already booked elsewhere, and a double booking costs the platform its credibility with both sides.

Availability therefore had to reflect the expert's external calendar continuously, in both directions: external commitments block Montelink slots, and Montelink bookings appear in the expert's own calendar. Anything less than two-way sync leaves a window where both systems disagree.

Video sessions as core infrastructure

For a consultation marketplace, the video call is the product being delivered. Handing a client a meeting link and hoping both sides show up leaves the most important part of the transaction outside the system.

The platform had to create each meeting, put it in both calendars, remind both parties before it starts, and connect the booking record to the session that actually took place, so billing has something real to measure against.

Turning payments into a revenue model

Every payment on Montelink is money a client owes an advisor. The platform's commission has to come out of that payment automatically on each paid order, with the gross amount, the commission, and the net payout recorded against the order.

Those figures also had to be visible to the advisor. An advisor who cannot check those numbers stops trusting the platform.

We designed and built the Montelink marketplace on Mercur, covering design, frontend, backend, and every external integration.

Marketplace architecture on Mercur

The platform runs on Mercur – our complete marketplace platform – providing the multi-vendor layer: expert onboarding, catalogue, cart, checkout, order management, admin, and multi-currency support.

Mercur's engine handled the whole marketplace mechanics, so development time went into custom features – the consultation-specific logic built on top rather than into rebuilding marketplace basics.

Montelink is a greenfield build. There was no legacy system to migrate, which meant the architecture could be shaped around minute-based consultations from the first commit.

Minute-based consultation billing

We built a custom billing engine that calculates the cost of a session from its duration. A client purchases a block of time at checkout, the system tracks the meeting against it, and any overage is charged automatically once the session ends.

No order is created when the card payment is declined, so a paid consultation cannot be booked without a successful charge.

This turns a variable-length service into something a commerce platform can transact. The client sees a price before booking, the expert is paid for the time they spent, and neither side has to reconcile the difference by hand.

Platform transaction fee, payout rules, and billing documents

The 5% platform fee is collected as a Stripe Connect application fee on every paid order, linked to that order and to the advisor's connected account. The advisor dashboard shows the order amount, the platform fee, and the net amount available for payout.

An advisor can request the next payout 7 days after the previous one, held both in the interface and at the API level, and the panel states the date the next payout unlocks.

Documents tab in the advisor panel carries subscription and commission invoices uploaded by the Montelink team, with an automatic email notification when a new document is available.

Expert panel with public profiles and credentials

Experts manage their own presence through a dedicated panel: onboarding, availability, pricing, reviews, and certificate upload. Uploaded credentials are previewable on the public profile, so a client can check an advisor's qualifications before booking one. Experts are responsible for the accuracy of the qualifications and credentials they publish.

The admin panel also supports featured experts and curated listings in each category.

Montelink's team is notified automatically on advisor registration, subscription purchase, renewal, and cancellation, so supply-side changes reach an operator without anyone watching a dashboard.

One checkout for consultations, webinars and e-books

Independent experts on Montelink offer three types of products: one-to-one paid consultations, group webinars, and digital products such as e-books. All three sit in the same catalogue and go through the same checkout, so a client moves between them without hitting a separate purchase flow for each.

Free consultations run down the same path. A zero-cost session is booked, scheduled, and delivered through the same infrastructure as a paid one.

AI translations with DeepL

We integrated the DeepL API to translate expert profiles and platform content automatically, rather than maintaining a separate copy per language. Machine-translated content is marked as such, and the original-language version remains the reference.

The translation layer runs on the frontend with edge caching, which keeps multilingual pages fast and removes manual translation work from the platform's operating cost.

Marketplace payouts via Stripe Connect Express

Each payment is split at the point of charge: the platform fee is deducted, and the remainder is credited to the expert's Stripe Connect Express account. Experts complete Stripe's onboarding once and request payouts from their panel – with no payment infrastructure of their own to build or operate.

VAT calculation with Stripe Tax

Stripe Tax calculates the applicable tax rate per transaction based on where the buyer and seller are. We integrated it to calculate EU VAT per transaction, including cross-border sales, so each consultation carries the applicable rate and the transaction records are available for reporting. Montelink displays the calculation provided by Stripe Tax.

Subscription plans with Stripe Billing

Stripe Billing handles recurring charges for platform access. We used it to run Montelink's subscription plans, including the usage limits attached to each tier. VAT is applied to each subscription automatically, based on the advisor's tax ID and country of registration.

Automated Zoom lifecycle

We integrated the Zoom API so the platform creates each meeting itself at the moment of booking, issues calendar invites to both client and expert, and sends time-based reminders before the session starts. The booking, the meeting, and the billing record are one chain.

Two-way calendar sync with Google Calendar and Outlook

We built two-way synchronisation with Google Calendar and Microsoft Outlook.

Commitments in an expert's own calendar remove the matching slots from Montelink, and consultations booked on Montelink appear in their calendar.

Clients only ever see slots the expert can genuinely take, which removes the double-booking problem without asking experts to maintain a separate availability schedule.

Hosting on Railway with AWS S3 storage

Railway hosts the application. AWS S3 stores uploaded certificates, invoices, and documents shared between clients and experts.

20% custom, 80% already in Mercur

Mercur supplied everything underneath that: expert onboarding, catalogue, cart, checkout, order management, and the multi-vendor logic. That covers around 80% of what any marketplace needs, leaving 20% as the custom work that makes Montelink itself.

Custom logic attaches to the core as modules with their own data models and services, so the consultation engine could be added without reaching into the marketplace underneath it or forfeiting future updates to it.

Built to open new markets without vendor lock-in

Multi-currency support is native in Mercur, and the translation layer covers platform content automatically, so adding a market is a configuration change. Montelink owns the platform outright, with no licence fees and no per-transaction cut going to a marketplace vendor as volume grows.

Automatic payment split and VAT calculation on every transaction

Mercur models every expert as an independent seller with their own commission terms, which is the structure the payment split and the tax calculation both hook into. An advisor sells across borders without operating payment infrastructure, and the applicable VAT rate is calculated for each sale automatically.