Seemingly OCI was installed with root user privileges. Installing the OCI with root privilege leaves the oci.so and 20-oci.ini files with the read permissions which the nginx user or group do not have access.

You need to update the file read permission of the OCI's .so file and .ini file that nginx can read those files and load when it processes a request.

It is assumed that your PHP-FPM is running with nginx user, too.