Have used version 2.0 and request seems like as below and used postman to test it
POST /v2.0/{guid}/InstallTest/api/v2.0/companies({compantid})/purchaseInvoices HTTP/1.1
Host: api.businesscentral.dynamics.com
Authorization: Basic username+password
Content-Type: application/json
Content-Length: 1049
{
"number": "107676",
"invoiceDate": "2020-04-10",
"postingDate": "2020-04-10",
"dueDate": "2020-04-30",
"vendorInvoiceNumber": "107210",
"vendorId": "9e3833b3-b1fd-ea11-bc7d-00155df3a615",
"vendorNumber": "20000",
"payToVendorId": "9e3833b3-b1fd-ea11-bc7d-00155df3a615",
"payToVendorNumber": "20000",
"shipToName": "",
"shipToContact": "",
"buyFromAddressLine1": "100 Day Drive",
"buyFromAddressLine2": "",
"buyFromCity": "Chicago",
"buyFromCountry": "US",
"buyFromState": "IL",
"buyFromPostCode": "61236",
"shipToAddressLine1": "7122 South Ashford Street",
"shipToAddressLine2": "Westminster",
"shipToCity": "Atlanta",
"shipToCountry": "US",
"shipToState": "",
"shipToPostCode": "31772",
"shortcutDimension1Code": "0002",
"shortcutDimension2Code": "ADM",
"currencyCode": "USD",
"pricesIncludeTax": false,
"discountAmount": 0,
"discountAppliedBeforeTax": true,
"totalAmountIncludingTax": 1911.82
}