document.requestStorageAccess() may not be called on a document with an opaque origin, such as a sandboxed iframe without allow-same-origin in its sandbox attribute.
Nid oes modd galw document.requestStorageAccess() ar ddogfen gyda tharddiad aneglur, fel iframe blwch tywod heb allow-same-origin yn ei briodweddau blwch tywod.