Attribution of maps is required. Per the Mapbox attribution requirements:
Static and print maps need to be attributed in the same fashion as you would cite a photograph: in a textual description near the image.
If you can include HTML, use this code snippet that includes links to Mapbox & OpenStreetMap:
© <a href='https://www.mapbox.com/about/maps/'>Mapbox</a> © <a href='https://www.openstreetmap.org/copyright'>OpenStreetMap</a> <strong><a href='https://www.mapbox.com/map-feedback/' target='_blank'>Improve this map</a></strong>
For print output or if you can’t include links, use this text-only attribution:
© Mapbox, © OpenStreetMap
Attribution of maps is required. See the Stadia Maps attribution and terms of service pages for details.
Commerical use is prohibited.