diff --git a/scripts/image-gen.ps1 b/scripts/image-gen.ps1
index e5ecfc7..bdfa4a9 100644
--- a/scripts/image-gen.ps1
+++ b/scripts/image-gen.ps1
@@ -79,7 +79,7 @@ $sw = [System.Diagnostics.Stopwatch]::StartNew()
 $r = $null
 
 # --- attempt 1: b64_json ---
-$body = @{ model = $resolvedModel; prompt = $Prompt; n = $N; size = $Size; response_format = 'b64_json' } | ConvertTo-Json -Depth 5
+$body = @{ model = $resolvedModel; prompt = $Prompt; n = $N; size = $Size; extra_body = @{ response_format = 'b64_json' } } | ConvertTo-Json -Depth 5
 try {
     $resp = Invoke-WebRequest -Uri $endpoint -Method Post -Headers @{ Authorization = "Bearer $resolvedKey" } -ContentType 'application/json; charset=utf-8' -Body $body -TimeoutSec $TimeoutSec
     $sw.Stop()
@@ -94,7 +94,7 @@ try {
     # Some providers reject b64_json; retry once with response_format=url.
     if ($status -eq 400 -or $status -eq 422) {
         Write-Err "WARN: b64_json rejected (status $status); retrying with response_format=url."
-        $bodyUrl = @{ model = $resolvedModel; prompt = $Prompt; n = $N; size = $Size; response_format = 'url' } | ConvertTo-Json -Depth 5
+        $bodyUrl = @{ model = $resolvedModel; prompt = $Prompt; n = $N; size = $Size; extra_body = @{ response_format = 'url' } } | ConvertTo-Json -Depth 5
         try {
             $sw.Restart()
             $resp = Invoke-WebRequest -Uri $endpoint -Method Post -Headers @{ Authorization = "Bearer $resolvedKey" } -ContentType 'application/json; charset=utf-8' -Body $bodyUrl -TimeoutSec $TimeoutSec