It is expected functionality if you're experiencing an error stating Failed as record(s) were not found. Error number 4 when attempting to change the service type on an existing service requirement.
You're unable to change the service type on a service requirement where the visits generated from the service requirement have been allocated or reconciled.
Instead, please end the existing requirement by entering an end date in the service requirement and start a new one with the correct service type. The Renew functionality could be used for this.
Alternatively, all the calls that need the service type updating can be unallocated and unreconciled, then the service type on the service requirement can be changed. Or, manually change the service type in each individual visit.