The most practical approach is starting with the single integration that covers the core transaction journey and evaluating it thoroughly before committing to it. Sandbox quality, certification timelines, and geographic coverage are all worth assessing before the architecture is locked in, since a provider mismatch at this stage tends to become a timeline problem. For most early-stage European fintech MVPs, a BaaS provider or a well-documented payment processor serves as the right starting point. Additional payment rails can be added as the product scales.