plugin zoom disables mobile pinch to zoom

Hi, my website has this code

<meta name=”viewport” content=”width=device-width,initial-scale=1,user-scalable=yes”>

it works on the whole website, also within the gallery. But if I click on a image to zoom it, this is no more possible. How can I enable the pinch to zoom when a gallery image is open? (depending on image proportions the ‘zoom’ is not always bigger on a smartphone and I need to zoom more)