If you fetch the job sessions for a job, the link for "log" is incorrect, have logged with Veeam which will hopefully patched in a future release.

Example

GET https://172.30.6.90:4443/v3/jobs/2a347af6-43ef-43a7-97bf-58a36f8cf216/jobsessions

[{"id": "9f4eba99-ce30-419b-a942-354744045f51","creationTime": "2019-06-16T22:00:00.0246404Z","endTime": "2019-06-16T22:09:26.9479152Z","progress": 21,"status": "Success","statistics": {"processingRateBytesPS": 98010,"processingRateItemsPS": 0,"readRateBytesPS": 1426172,"writeRateBytesPS": 31686381,"transferredDataBytes": 55561549,"processedObjects": 523,"bottleneck": "Source"},"_links": {"self": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51"},"log": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51/log"},"job": {"href": "https://172.30.6.90:4443/v3/jobs/2a347af6-43ef-43a7-97bf-58a36f8cf216"}}}]

Noting that the _links section has a log link as below

https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51/log

This returns a 404

As per the documentation this should be LogItems

for example https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51/LogItems

Which then returns the results as expected

{"offset": 0,"limit": 30,"results": [{"id": "35de947e-4512-4e71-8be4-1471d84ae21d","usn": 1,"title": "[Success] Job started at 17/06/2019 10:00:00 AM","creationTime": "2019-06-16T15:00:00.0402129-07:00","endTime": "2019-06-16T15:00:00.0402129-07:00","_links": {"self": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51/logitems/35de947e-4512-4e71-8be4-1471d84ae21d"},"jobsessions": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51"}}},{"id": "c7347833-6127-4a50-b3cc-9a0b5dcbcf99","usn": 2,"title": "[Success] Connected to organization","creationTime": "2019-06-16T15:00:00.0558112-07:00","endTime": "2019-06-16T15:00:06.3683425-07:00","_links": {"self": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51/logitems/c7347833-6127-4a50-b3cc-9a0b5dcbcf99"},"jobsessions": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51"}}},{"id": "231e6102-46c7-4abe-a4bc-c017e51d2da2","usn": 1000,"title": "[Success] Found 491 excluded objects","creationTime": "2019-06-16T15:00:06.3683425-07:00","endTime": "2019-06-16T15:08:02.6508329-07:00","_links": {"self": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51/logitems/231e6102-46c7-4abe-a4bc-c017e51d2da2"},"jobsessions": {"href": "https://172.30.6.90:4443/v3/jobsessions/9f4eba99-ce30-419b-a942-354744045f51"}}}....