which countries do I enter for the question about business activities

Countries of establishment, not countries of turnover

This question is almost always about the countries where the enterprise has an establishment: an office, a factory, a branch with its own address. Not about countries where a customer happens to be located or where a product is delivered. A Dutch enterprise that exports to Germany and Belgium, but has no establishment there, enters only the Netherlands. As soon as there is a subsidiary, branch or secondary establishment registered abroad, that country goes on the list.

The source for this is the same as for the question in which countries does the company have operations: the extract from the business register, or the overview of secondary establishments that comes with it. If you are unsure whether a foreign activity is an establishment or only a sales channel, check whether a local registration exists — no registration usually means no establishment in the sense of this question. This topic also relates to the question in which sector the undertaking operates: some portals ask sector and country in combination, because a customer wants to know whether a risk is regional or spread across multiple countries.

Basis: the business register per establishment

The Trade Register Act 2007 provides that every establishment of an enterprise — head office and secondary establishment — with its own address and country is registered. That register is the first place to check which countries are correct, before you enter anything in a customer portal; not the enterprise's own impression of where the business is "active". For groups with multiple legal entities in different countries, registration in each country runs via the local chamber of commerce or its equivalent, and those separate extracts together form the answer to this question.