I am doing a simple fetch upon button click to my api:

async function UpdateEscrow(){

        let testmerchID = 'mer_960728a76ae2';
        let url = 'https://api.onlinebetaalplatform.nl/v1/merchants/'+testmerchID // test merchant
        let apikey = 'asd';
        
        fetch(url, {
            headers: {Authentication: 'Bearer '+apikey}
          })
             .then(resp => resp.json())
             .then( json => console.log(json))
                
    }

But it fails, stating that cross origin is not allowed and it wont read from an external resource (the url).

However, I am alredy doing rest calls to another api we have connected and those work fine.

Why is this one blocked?