well. you can also do it the other way around and charge the same price but the VAT component changes. -e.g. 5€ gross price will result in different net prices depending on the buyers location. hence slight differences in the margin for you

You also have to display the VAT rate and share of the price. So this won't help much.

That's easy to work around, just set the total price to the maximum for all possible rates. It does mean that you're pocketing more revenue from countries with lower sales tax rates, but makes it simpler to manage in the front end.

The calculation to make is will you lose in terms of total profit by charging people in Luxembourg 24% more than you would otherwise (3% sales tax vs 27% VAT in Hungary)?

But you probably don't have to show that level of detail until the payment stage, by which time hopefully you do have enough information to determine it.

In contrast, consumer protection laws in various EU states require that the price shown is the full tax-inclusive price throughout, even if it's in big numbers right there on your home page.

it's less about the payment processing but about the invoicing and billing itself. anyways, it means more complexity for start ups in the EU which sucks

Yes, well, I used "payment processing" as an umbrella term here.

Because what you mention is in fact one of the things that people often only realise after they're already halfway into implementing a pretty Stripe binding; "Oh, oops, we have to send proper invoices, too". And then "Oh, dunning, pro-rating, etc. turns out a lot more complex than I thought".

I've been there a few times, it can be done, but it has been a nightmare every single time.

Agreed accounting/payment processing is a crazy time sink. On the other hand, I'm not aware of any on-line payment service or marketplace site that could even support all the fundamental requirements for a lot of start-up business models to comply with the new rules right now without doing a significant degree of additional integration or customisation work anyway.

For example, it's all very well having the payment service work out the actual VAT and do the invoicing, but under existing consumer protection laws in various EU states you still have to show the tax-inclusive price throughout. That immediately means you can no longer display a static price on your web site, if you add VAT at the appropriate local rate to a fixed base price rather than having a fixed total price paid by the customer and then taking a different VAT hit internally depending on where each customer is.