To use multiple inbound routes, you can use the default vault inbound endpoint "https://<vault id>.SANDBOX.verygoodproxy.com" for the first inbound route. No CNAME is needed to be added for the first inbound route, this is "Default" option already set under the Routes > Inbound > Manage button > from under the Custom Hostnames section.
When creating an additional inbound route you will need to add a CNAME. Remove the "Default" CNAME if you are using it as an endpoint on the first inbound route. By adding a CNAME you are distinguishing between the first route and the second route with the a unique CNAME. For every additional inbound route, you will need to set another unique CNAME to distinguish it from the previous inbound routes.
NOTE 1: Remember to add the CNAME under Vault Settings > Custom Hostnames tab > Add button.
NOTE 2: Remember to apply the CNAME under each inbound route from Routes > Inbound > Manage button > add the CNAME from under the Custom Hostnames section.