I have added an EZproxy stanza but off-campus access to the resource still does not work

We authenticate and the correct proxy-prefix is added to the target URL but the resource does not recognize us.

Is the problem with the stanza? If you find that the Starting Point URL resolves correctly then this is most likely an issue with the providers' registration of your EZproxy server.

E.g. say you start with the Starting Point URL: https://ezproxy.institution.com/login?url=www.somedb.com/

and this resolves to: https://www-somedb-com.ezproxy.institution.com/

This shows that the EZproxy stanza is OK - it has stayed in proxy (hence the EZproxy domain included in the first part of the resolved URL) & has dealt with the https stanza (hence the hyphens in www-somedb-com, which EZproxy uses to allow the EZproxy servers certificate to not generate errors).
If your stanzas are not resolving correctly as above, then you need to check/correct the stanzas.
If your stanzas are resolving correctly, then the problem is usually that the provider has not registered your EZproxy server's IP address correctly & you will have to contact them to get this resolved.
Tip: if your EZproxy is installed on a Windows server, then open a browser on the server, use a GeoIP site & screenshot the IP address, then open the target URL without the EZproxy part of the Starting Point URL, so that the EZproxy software is not involved & again screenshot the results, then send the screenshots to the providers.

12860