SLES 12.5 BYOL- need to add LTSS but getting error

We are having few machine those are having SLES 12.5 and BYOL. Now we want to enable LTSS on it. we got the registration code but while registration we are getting below error.

# SUSEConnect -r XXXXXXXXXXXXXXX
Registering system to SUSE Customer Center

Announcing system to https://scc.suse.com

Activating SLES 12.5 x86_64 …
Error: Registration server returned ‘The subscription with registration code ‘XXXXXXXXXXXX’ does not include the requested product ‘SUSE Linux Enterprise Server 12 SP5 x86_64’’ (422).

I tried to clean it and again reregister but same error. Could you please suggest how to enable the LTSS.

Thanks in advance