@Mark Thanks for your question. I have tested from my end, and I was able to create budget using REST API. For your reference, I have shared the request body of the REST API. Kindly retry the REST API operation and revert if you have further questions.
{
"eTag": "\"1d34d016a593709\"",
"properties": {
"category": "Cost",
"amount": 100.65,
"timeGrain": "Monthly",
"timePeriod": {
"startDate": "2022-05-01T00:00:00Z",
"endDate": "2022-05-31T00:00:00Z"
},
"notifications": {
"Actual_GreaterThan_80_Percent": {
"enabled": true,
"operator": "GreaterThan",
"threshold": 80,
"locale": "en-us",
"contactEmails": [
"xxxxxxx@microsoft.com"
],
"contactRoles": [
"Contributor",
"Reader"
]
"thresholdType": "Actual"
}
}
}
}
Image for your reference.
I assume you are not adding below properties within your request body which are mandatory to create the budget alert.
- properties.amount
- properties.category
- properties.timeGrain
- properties.timePeriod