Leaglise marriage certificate for Schengen visas?

[szcad]

My husband(British and French dual nationality) and I (Chinese passport)got married in the Uk and has a Uk marriage certificate.

I have applied for the Eu spouse visa and have plans to go to Spain in May. They accepted my application but warned me that I should get French official to legalise the marriage certificate. Otherwise I will get fined or something VidMate.

We are planning to go to London in May as well, could drop off to visit the French embassy and get it done but just wondering if we need to do it before they assessed the visa application or just before next visa application?

Thank you in advance