Engine cranks, will not start

Ignition key turns to start, vehicle continues to crank but will not turn over.

-New battery and hang tested another battery. Battery has tested fine.

-Alternator tested and passed 2/3 time with decent recharge.

-Starter tested, no issues.

-Tested spark plugs, no issues.

-Tested and cleaned fuel injectors and fuel rail, no issues.

-Cleaned intake manifold, airflow seems fine. Took a VAST amount of carburetor cleaner and sprayed into the manifold, engine fired about once or twice and immediately stopped.

-Fuses and relays, all with no issues, ASD and HVAC fuses replaced just off a hunch from browsing forums online and recommendation. Did not resolve the issue.

-Checked most of the visible wiring and no obvious issues.

- Internal OBD-II gave a trouble code for the oil pressure sensor, replaced sensor and cleaned connection. Code went away.

- New code populated (OBD-II trouble code P0688: ECM/PCM power relay sense circuit/open) P0688 means there is an output circuit issue in the power relay sense circuit, likely due to a damaged or defective ECM relay or faulty wiring.

Does anyone have recommendation on how exactly to test this? Is this really an issue that would cause it to mechanically fail?

All and any help is greatly appreciated!