what can this error mean and how to resolve this error in Lightspeed (i.e. check the shop ID or register ID).
By us it's alreay back OK, after we restart the API.
It means you have to specify the shopID and the registerID in the payload.
All Sales essentially must be assigned to a specific location and register and so your code needs take note of that and insert them accordingly
An example of how to make Sales using the API can be found here:
Integrations & Solutions Developer - Strategic Solutions