Hi @radjr
Have you also double checked if the IP address of that user is correct i.e. in the range defined for that institutional subscription? – Maybe a proxy is used, so that IP addresses are different…
See maybe also this explanation about X-Forwarded-For headers: XFF headers supported in OJS 2.4.x - #3 by radjr
What OJS version are you using?
OJS does not have any log files (just the usage statistics plugin log files, if enabled/set) i.e. one would probably need the server (e.g. apache) log files… Also probably a more detailed debugging/logging would be needed…
See also maybe other posts in this forum, e.g.: Problems activating Institutional Subscriptions for proxy servers - #5 by Enzo
Best,
Bozana