When a service is associated with a organisation set the free allowance to

the default free allowance for the organisation type.

The update/insert for the default free allowance is done in a separate
transaction. Updates to services need to happen in a transaction to
trigger the insert into the ServicesHistory table. For that reason the
call to set_default_free_allowance_for_service is done after the service
is updated.
I've added a try/except around the set_default_free_allowance_for_service call to ensure we still get the update to the service but get an exception log if the update to annual_billing fails. I believe it's important to preserve the update to the service in the unlikely event that the annual_billing upsert fails.

app/organisation/rest.py

@@ -1,8 +1,9 @@
 
 from flask import Blueprint, abort, current_app, jsonify, request
-from sqlalchemy.exc import IntegrityError
+from sqlalchemy.exc import IntegrityError, SQLAlchemyError
 
 from app.config import QueueNames
+from app.dao.annual_billing_dao import set_default_free_allowance_for_service
 from app.dao.fact_billing_dao import fetch_usage_year_for_organisation
 from app.dao.organisation_dao import (
     dao_add_service_to_organisation,
@@ -119,6 +120,16 @@ def link_service_to_organisation(organisation_id):
     service.organisation = None
 
     dao_add_service_to_organisation(service, organisation_id)
+    # Need to do the annual billing update in a separate transaction because the both the
+    # dao_add_service_to_organisation and set_default_free_allowance_for_service are wrapped in a transaction.
+    # Catch and report an error if the annual billing doesn't happen - but don't rollback the service update.
+    try:
+        set_default_free_allowance_for_service(service, year_start=None)
+    except SQLAlchemyError:
+        # No need to worry about key errors because service.organisation_type has a foreign key to organisation_types
+        current_app.logger.exception(
+            f"Exception caught when trying to update annual billing when the organisation "
+            f"changed for service: {service.id} to organisation: {organisation_id}")
 
     return '', 204