From your 2021 MCME Centralized Patching precourse:
A patch failure is when you are unable to reach a physician after trying both the primary and secondary BHP phone lines. In these situations, proceed with treatment if the treatment is outlined within the ALS PCS directives (or in the case of cardiac arrest, proceed with transportation) and attempt to establish communication when feasible.
Should this happen, please let us know so that we can examine what happened and try to improve the system. Please document this patch failure on your ACR and complete and online self-report to flag this.
It is reasonable to try the primary line a second time, before attempting the secondary line. Sometimes the Primary BHP cannot answer the phone quickly enough.