precreate-git-repos-auth.ps1

$auth = "apitest:j2vsnu3obx55ekwjkfdxfpljziiy27qkuku5jitsx73wvegpdpeq"
$bytes = [System.Text.Encoding]::ASCII.GetBytes($auth)
$token = [System.Convert]::ToBase64String($bytes) 
$headers = @{ Authorization = "Basic $token" }

precreate-git-repos-azuredevops.ps1

$org = "tolle" # my sandbox Azure DevOps organization
$url = "https://dev.azure.com/$org/_apis/git/repositories?api-version=6.0"
# $projectId = "288c25f0-4bc9-4139-9337-cdbb328f1af8"
@("repo001", "repo002", "repo003") | ForEach-Object {
    $name = $_
    $body = @"
{
    "name": "$name",
    "project": {
        "id": "$projectId"
    }
}
"@
    Invoke-WebRequest -Uri $url -Method POST -Headers $headers -Body $body -ContentType "application/json" 
}

precreate-git-repos-projectid.ps1

$org = "tolle"
$url = "https://dev.azure.com/$org/_apis/projects?api-version=6.0"
$projectCall = Invoke-WebRequest -Uri $url -Method GET -Headers $headers
$projects = $projectCall | ConvertFrom-Json | Select-Object -ExpandProperty value
$projectName = "try-api" # the current Azure DevOps project 
$project = $projects | Where-Object { $_.name -eq $projectName }
$projectId = $project.id