Add credit open street map

Hello,

I have an open street map displayed on my website.

Here is the url : https://www.biotope-environnement.be/#references

I added the attribution link on the bottom right corner but I still have the notice "Attribution is not optional" showing on my map. To display the credit, I edited the js file that generates the map, I added the link in the setting "Attribution".

Did I miss something ?

Many thanks