API graph access

Followed instructions / examples for the graph API here https://docs.observium.org/graph_api/

But it seams I'm having issues retrieving any graphs.

The binary data retrieved via curl when saved doesn't show any graphs but errors. (images attached for reference)

However when I take the URL itself and paste it into the address bar of Firefox I can see the graph image for the port_bits but not the multiport_bits one.

The API calls I'm using:

for port_bits:

curl -s -o dot.png -u user:pass  http://<host IP>/graph.php?type=port_bits&id=2740&period=2629746&height=300&width=1220

for multiport_bits:

curl -s -o dotmulti.png -u user:pass  http://<host IP>/graph.php?type=multiport_bits&id=2740&period=2629746&height=300&width=1220

Can someone please indicate what I might be doing wrong.