CPF1941 when trying to add a SEP

Does anyone know what this actually means?

I want to add a service entry point on a program I just compiled. The debug server and service show as active.

I click the + button on the Service Entry Points panel, type my program name `FMLCL/PRSMQLOG`, and press Enter.

I get a pop-up error dialogue and the error it shows is reflected in the Output tab.
```
DBGM0006E Failed to set service entry point on FMLCL/PRSMQLOG *PGM.
Reason: Server: CPF1941 Serviced job has completed. Debug commands are not allowed.
```
It doesn't make any sense to me. I'm not trying to service a job. Nor have I been previously. I'm just trying to set the SEP. I swear I have done this before, but it just doesn't want to work for me now.

This has happened on two different days, in between which the LPAR concenred was even IPLed. Likewise VSCode has been stopped and started.