При ошибке Classic styles are no longer supported; see https://blog.mapbox.com/deprecating-studio-classic-styles-d8892ac38cb4 for more information
Заменить
L.tileLayer('https://api.tiles.mapbox.com/v4/{id}/{z}/{x}/{y}.png?access_token={accessToken}',{
attribution: 'Map data © <a href="https://www.openstreetmap.org/">OpenStreetMap</a> contributors, <a href="https://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>, Imagery © <a href="https://www.mapbox.com/">Mapbox</a>',
maxZoom:18,
id:'mapbox.streets',
accessToken:'YOUR_MAPBOX_ACCESS_TOKEN'
}).addTo(mymap);
на
L.tileLayer('https://api.mapbox.com/styles/v1/{id}/tiles/{z}/{x}/{y}?access_token={accessToken}',{
attribution: '© <a href="https://www.mapbox.com/about/maps/">Mapbox</a> © <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a> <strong><a href="https://www.mapbox.com/map-feedback/" target="_blank" rel="noopener noreferrer">Improve this map</a></strong>',
tileSize:512,
maxZoom:18,
zoomOffset:-1,
id:'mapbox/streets-v11',
accessToken:'YOUR_MAPBOX_ACCESS_TOKEN'
}).addTo(mymap);