Here is the thing almost no blog tells a Nigerian applicant. Spain requires every DNV holder to be covered by social security, and there are exactly two ways to satisfy it: a certificate of coverage under a bilateral social-security agreement between Spain and your employer's country — or your employer registering with Spanish Social Security and affiliating you. Spain has no social-security agreement with Nigeria.

What that means in practice:

If you're an employee of a Nigerian (or other no-agreement-country) company: your employer must be willing to register itself with Spanish Social Security and pay contributions for you — a real legal and financial commitment few foreign employers accept for one worker.
If your employer is in an agreement country (much of Europe and Latin America, and others): the employer obtains a certificate of coverage for teleworkers — clean and doable. Ask which country pays you before assuming.
If you're self-employed: the wall isn't there — you commit to registering as [[autónomo|Spain's self-employed status. You register with the tax agency (Hacienda) and social security (RETA), pay monthly contributions, and invoice clients legally from Spain]] in Spain yourself, which is entirely in your own hands.

The honest conclusion for most Nigerians: the self-employed lane is the practical one. Freelancers, consultants and contractors — with clients abroad and contracts at least three months old — hold the keys to their own application. Employees of Nigerian companies should have the frank conversation with their employer first, before spending a naira on documents.