I get a notification that this number does not exist. iOS previously had the option to format numbers this way. They have now removed that option to format numbers like this. If you've been using your contacts via iCloud for your new phone for years, you might have such numbers in your contacts. We therefore recommend noting these numbers without the (0), resulting in +31612345678. That number can then be called.
But if I call via my phone, that number CAN be called.
That's correct! That could indeed be the case. We have chosen not to allow calling with this number format. Here's why: Our app ignores spaces, parentheses, hyphens, etc. But we don't program our app to ignore numbers. This is because there are various rules about number formatting throughout Europe. For example, in Spain it's quite normal not to show the first 0 of a number like 0612345678. If we were to tell our app to ignore certain numbers in some situations, we would create bigger problems than we'd solve. That's why we choose not to accept formats that are 'not logical' in our formula for reading phone numbers. In this case, the +31 already replaces the 0, and the 0 replaces the +31, so including both is 'not logical'.