Working 100% remote for German company out of Spain

Hi all,
Been googling for 2 days now trying to find my specific case. So far haven't yet found an exact match so I ll try here.

I ve been working for a German company (I relocated to Berlin) for the last two years.
Couple weeks ago I got the good news that I would be allowed to go full remote starting 2020.

We're thinking about moving to Spain (or France) so I'll still be working full time for the German company and get a salary from them.

We still have a house in Belgium that we will keep (and not rent out for now) which we will be visiting every once in a while.

What would it take to fall under the Beckham Law and get a flat tax rate of 24%?

The German company can still be 'molded' into a certain arrangement that would be most optimal for me (while being quite easy to implement for them)

Thank you

I cant seem to be able to edit a post so I ll put it here:

Concerning Beckham Law only applying when you are actually employed by a Spanish company, this doesn't seem to be the case anymore, according to a post on http://tax-free.today

"Under the new system, it’s no longer necessary for expat workers to be employed in Spain; they can also be dispatched to Spain while receiving their whole salary from abroad."

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