Working as freelance service technician in other EU countries?

[Hasi97]

Hi all, 

I have been working as freelance service technician for a year and half. During this time my client as expanded to other countries such Germany, France and Spain. I was wondering what documents I would be required to have in order to be able to provide my services in these countries. My client is a dutch company and all invoices go to the dutch identity. As far as I know there is free movement of goods and services in BENELUX and no additional documents are required. 
Is the A1 declaration sufficient from SVB? 
Is the EU declaration required? 

[Joost Rietveld]

The best source for this is probably your cliënt. If they set up shop in another country and they want to hire you in those countries as well, then it would be reasonable from them to sort this out.