Marketplace Payments Integration Guide: Challenges and Solutions

How onboarding can be a bottleneck

In one project for a UK-based B2B marketplace, onboarding a corporate seller turned into a weeks-long ordeal. Stripe Connect required ID verification for aa lot of shareholders. One was a retired stakeholder the client hadn’t contacted in years.
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Despite the business being reputable, payouts were blocked. We had to walk the client through options like:

• Using Stripe Standard accounts
• Connecting an existing Stripe account
• Exploring managed onboarding through a support channel

This experience taught us that when working with larger sellers, you need to plan for KYC slowdowns.
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Missing Credentials

During one of our marketplace projects, the client chose Adyen for Platforms. Everything was on track, until they tried to create test marketplace accounts. Nothing worked.

After digging in, we discovered the issue: Adyen’s special “MarketPlace” API credentials hadn’t been provisioned.

These credentials aren’t included by default. We submitted a request on the client’s behalf—and waited. For two weeks, there was no response. The delay put the entire integration on hold and pushed back the delivery timeline.

Always request credentials early and, if possible, work through an Adyen account manager rather than generic support. That one small detail can save weeks.

Documentation Don't Tell You Everything

Official docs rarely cover edge cases. In one Stripe-based build, we struggled with an unclear webhook behavior. The fix? A GitHub issue from another developer who hit the same bug and shared a workaround involving a minor SDK version rollback.
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In another case, we were debugging PayPal integration in OpenCart and couldn’t find the issue, until we saw a forum thread that pointed to a caching plugin conflict.
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Now let's turn to the most common payment integration issues that are widely spread in the dev community. 

Integrating payment gateways like often leads to recurring API issues. Developers usually face misconfigured credentials, version mismatches, and sandbox/production confusion.

For example, using Stripe’s API with the wrong version or webhook settings can throw exceptions.

One developer reported a .NET version mismatch error on Stack Overflow.



Even established providers aren’t immune to instability. In November 2024, PayPal’s Braintree API experienced a global outage. Merchants saw HTTP 500 errors, failed transactions, and blocked withdrawals for hours. This caused revenue losses and damaged trust.

To reduce risk, marketplace platforms must design with resilience in mind:

• Put in place robust error logging
• Track API versioning
• Set up fallback systems for downtime
• Check integration health

You see, that these common pitfalls show how fragile integrations can become without safeguards. 

Security is a critical concern in marketplace payment integration. Platforms face unique risks. They process high volumes and often act as intermediaries - an ideal target for fraud.

Payment fraud and chargebacks

Stolen credit cards and fraudulent buyers cause chargebacks. One rising threat is Authorized Push Payment (APP) fraud. In this scam, users are tricked into making payments themselves.

According to The Paypers, €2.4 billion in APP fraud losses in Europe come from marketplaces, often on large tech platforms.

Marketplaces operate under complex legal frameworks in both Europe and the United States. This reflects how platforms onboard users, move money, and manage risk.

KYC, KYB, and AML Obligations

Users must verify their identity, to send or receive money. That’s the law.
That rule applies across providers like Stripe, PayPal, Adyen, Mangopay. Platforms must collect:

• Full legal names
• Date of birth and government ID
• Business ownership details (for KYB)
• Bank account information

For casual sellers, this adds friction. For large companies, it creates real blockers.

Unfortunately, there’s no easy way around it. Even trusted sellers must submit paperwork, or payouts will be frozen.

Laws like IRS 1099-K, DAC7, and AML directives demand full transparency. If you run a marketplace, you must collect and verify user information. Period.

Licensing and Money Transmission

In the US, transmitting funds may classify your platform as a Money Services Business (MSB). That requires licenses across many states under FinCEN rules. In the EU, PSD2 mandates licenses for platforms executing payments.

To avoid this, most marketplaces rely on licensed intermediaries. For example Stripe Connect, Adyen for Platforms, Mangopay. These providers carry the license. The marketplace acts as their agent.

Data Privacy: GDPR, CCPA, and Beyond

Marketplaces process sensitive data: names, addresses, payment details. That is why you must:

• Encrypt all traffic (HTTPS)
• Avoid logging raw payment data
• Limit storage to PCI DSS-compliant tokens
• Respect data minimization and retention rules

If you use fraud detection APIs or offshore support, you must check data transfer compliance under GDPR or CCPA. Legal and compliance teams should review integration flows and third-party services.

A common mistake? Forgetting that a simple log entry with unmasked card data can violate multiple laws.

PSD2, PSD3, and Digital Resilience

PSD2 changed how European marketplaces handle payments. Since 2021, Strong Customer Authentication (SCA) is mandatory. Most platforms now use 3D Secure 2, which adds friction at checkout. If not implemented cleanly, it leads to abandoned carts.

By 2024, SCA is standard, but PSD3 is already in the pipeline. It may tighten rules around open banking, BigTech, and fraud detection.

Additionally, the Digital Operational Resilience Act (DORA) will soon apply to large fintechs and platforms. For you this means:

• Annual penetration testing
• Detailed incident reporting
• Stronger ICT risk controls

In 2025, marketplace operators must treat operational resilience as seriously as financial compliance.

PCI DSS and Card Security

Most platforms avoid PCI DSS scope by using tokenized fields (e.g., Stripe Elements or Braintree Drop-In). But mistakes happen.

If you log card numbers in dev mode, store raw CVVs, or handle payments on your server, you enter PCI scope. That means:

• Network scans
• Security questionnaires
• Risk of audits

The safest path? Use provider-hosted solutions. Never process raw card data. And never assume your logs are clean unless you check.

Many providers now advertise compliance as a feature. For example, Tipalti, Mangopay, and Adyen highlight automated onboarding and fraud detection.

But even with great tools, the responsibility is yours. Communicate clearly with your sellers. Guide them through the process. 

​For teams that want to skip months of custom development and get to market faster, a white-label marketplace platform can reduce compliance risk and accelerate go-live

The most successful marketplace platforms treat payment integration as a product experience, not just a backend process. They collaborate across engineering, product, and compliance teams to ensure the payment flow is:

• Technically robust
• Legally sound
• Transparent to sellers
• Seamless for buyers

At Ulan Software, we help companies plan, build, and launch global platforms through our online marketplace development services, from back-end architecture to seamless payment integration.

If you're building or scaling a multi-vendor marketplace and want to get payments right from day one, let’s talk.