Is that you must use sandbox?
From the log, do you see SMACK issue like below?
Apr 15 15:21:34 swi-mdm9x28-wp user.info Legato: INFO | httpGet[2472] | HTTP Get!
Apr 15 15:21:34 swi-mdm9x28-wp user.notice kernel: [ 562.769934] audit: type=1400 audit(1586935294.631:9): lsm=SMACK fn=smack_inode_getattr action=denied subject="app.http_get_WP76" object="admin" requested=r pid=2472 comm="httpGet" path="pipe:[11977]" dev="pipefs" ino=11977
Apr 15 07:21:34 swi-mdm9x28-wp user.err Legato: =ERR= | httpGet[2472]/httpGetComponent T=main | httpGet.c GetUrl() 79 | curl_easy_perform() failed: Couldn't resolve host name
If so, you might need to change the /etc/resolv.conf
permission