Discrepancy between the Dimensions & Metrics explorer and Analytics API - google-analytics

Question

There appears to be a discrepancy between the Dimensions & metrics explorer and the Analytics API v4. When adding the metric Transaction revenue together with Product name, SKU, item quantity and unique purchases yields the response
{
"error": {
"code": 400,
"message": "Selected dimensions and metrics cannot be queried together.",
"status": "INVALID_ARGUMENT"
}
}
even though according to the Dimensions & metrics explorer, they should be compatible.
You can try this yourself by visiting https://developers.google.com/analytics/devguides/reporting/core/dimsmets and checking the following dimensions/metrics from the Ecommerce category: ga:ProductSKU, ga:productName, ga:transactionRevenue, ga:itemQuantity and ga:uniquePurchases. The explorer should gray out incompatible dimensions and metrics as you select them but Transaction revenue is shown to be compatible.
I run the query using the endpoint https://analyticsreporting.googleapis.com/v4/reports:batchGet with the following JSON body. I've redacted the view id from the pasted body:
{
"reportRequests":[
{
"viewId":"[REDACTED]",
"dateRanges":[
{
"startDate":"2019-01-01",
"endDate":"2019-03-29"
}
],
"metrics":[
{
"expression":"ga:itemQuantity"
},
{
"expression":"ga:transactionRevenue"
},
{
"expression":"ga:uniquePurchases"
}
],
"dimensions":[
{
"name":"ga:productName"
},
{
"name":"ga:productSku"
}
],
"orderBys":[
{
"fieldName":"ga:itemQuantity",
"sortOrder":"DESCENDING"
}
],
"samplingLevel":"LARGE",
"segments":[],
"pageSize":100000,
"hideTotals":true,
"hideValueRanges":true,
"includeEmptyRows":true
}
]
}
According to the Dimensions & metrics explorer the above query should be OK but it yields the aforementioned 400 response. Removing ga:transactionRevenue from the JSON body yields a valid 200 OK response containing the report based on the parameters listed in the above JSON.
Is there something I'm missing here or is there an error in the explorer combinations?