The information in English on the government website.
Guide from the Tax Office on how to register with you’re using CSV
COVID-19 information:
What if I want to use the ‘invitation letter’ to register, but I´ve changed address?
Then you need to communicate your change of address first, through Modelo 036 or 037 when you are Autonomo
or through Modelo 030 if you are a private individual. Both links direct to a special protocol in place during the State of Alarm.
I have requested the invitation letter to register with Cl@ve but it has not arrived. What should I do?
When you do not have a Cl@ve PIN, digital certificate or electronic DNI, you must access through the REN0 service, registering a reference number, and check your address. Access the REN0 service to obtain a reference number through the following link: