Somewhere between Amsterdam and Berlin, your phone doesn't know it's crossed a border. It shouldn't have to, and if you've set things up right, it won't ask.
Multi-country trips are the case travel eSIMs were built for, but they're also where people quietly overspend - a Dutch plan for four days, then a German one for the next six, then finding out afterwards that a regional option covered both the whole time. It happens on the obvious routes too: a Benelux long weekend, a Balkan loop through three or four borders in a fortnight, an Iberian coast drive that drifts from Portugal into Spain without anyone deciding to cross. Here's the how-to version, once.
Country plan vs regional plan
A country plan covers one destination named in the plan and nothing past its border. Cross into a second country still on it, and you're roaming outside the plan's boundary at that country's own rates, not the price you saw at checkout. A regional plan bundles a set of countries under one data pool, priced and sold as a single trip.
The rule of thumb: if your itinerary crosses two or more borders, check the regional list before the country list. It's almost always cheaper than paying twice, and it removes the swap-at-the-border step entirely.