For instance in France, it has been mandatory to use such compliant software since 2018 for all companies.
For instance in France, it has been mandatory to use such compliant software since 2018 for all companies.
Not really. Well, only if you are a really really small company (read below VAT threshold).
Once you're VAT registered the tax authorities will want the irrevocability.
However, having said that the complexity in doing small business accounting (at least here in Poland) is not in generating invoices, but in accounting for them correctly with regards to VAT. Is this just a domestic sale/purchase? Is it an EU goods or services purchase/sale? Is it the same but for outside EU? Is the client a company or an individual? Does he/she want to return a item. Did you send an invoice, but never got paid? (you're still on the hook for the VAT) All those things matter and affect how you're supposed to record your VAT. In many cases of cross border transactions you end up recording VAT in a special way so it cancels out, but you need to report the right amounts. The logic to not mess this up is what makes people pay for this software. There is nothing stopping you doing all of it in Excel if you want, but if you mess up... It might be expensive.
My brother-in-law, Wallace, in the back office, is a system compliant with all of those constraints.