diff --git a/tariff/ostrom.go b/tariff/ostrom.go
index 4f4e582a2..f71b69376 100644
--- a/tariff/ostrom.go
+++ b/tariff/ostrom.go
@@ -25,6 +25,7 @@ type Ostrom struct {
 	*embed
 	*request.Helper
 	log          *util.Logger
+	env          string
 	zip          string
 	contractType string
 	cityId       int // Required for the Fair tariff types
@@ -42,7 +43,7 @@ func init() {
 func ensureContractEx(cid int64, contracts []ostrom.Contract) (ostrom.Contract, error) {
 	var zero ostrom.Contract
 
-	if cid != -1 {
+	if cid != 0 {
 		// cid defined
 		for _, contract := range contracts {
 			if cid == contract.Id {
@@ -58,13 +59,15 @@ func ensureContractEx(cid int64, contracts []ostrom.Contract) (ostrom.Contract,
 }
 
 func NewOstromFromConfig(other map[string]any) (api.Tariff, error) {
-	var cc struct {
+	cc := struct {
 		ClientId     string
 		ClientSecret string
+		Environment  string
 		Contract     int64
+	}{
+		Environment: "production",
 	}
 
-	cc.Contract = -1
 	if err := util.DecodeOther(other, &cc); err != nil {
 		return nil, err
 	}
@@ -78,6 +81,7 @@ func NewOstromFromConfig(other map[string]any) (api.Tariff, error) {
 
 	t := &Ostrom{
 		log:    log,
+		env:    cc.Environment,
 		basic:  basic,
 		Helper: request.NewHelper(log),
 		data:   util.NewMonitor[api.Rates](2 * time.Hour),
@@ -123,10 +127,26 @@ func NewOstromFromConfig(other map[string]any) (api.Tariff, error) {
 	return t, nil
 }
 
+func (t *Ostrom) apiUri(path string) string {
+	uri := ostrom.URI_API_PRODUCTION
+	if t.env == "sandbox" {
+		uri = ostrom.URI_API_SANDBOX
+	}
+	return uri + path
+}
+
+func (t *Ostrom) authUri(path string) string {
+	uri := ostrom.URI_AUTH_PRODUCTION
+	if t.env == "sandbox" {
+		uri = ostrom.URI_AUTH_SANDBOX
+	}
+	return uri + path
+}
+
 func (t *Ostrom) getContracts() ([]ostrom.Contract, error) {
 	var res ostrom.Contracts
 
-	uri := ostrom.URI_API + "/contracts"
+	uri := t.apiUri("/contracts")
 	err := t.GetJSON(uri, &res)
 	return res.Data, err
 }
@@ -164,7 +184,7 @@ func (t *Ostrom) getFixedPrice() (float64, error) {
 }
 
 func (t *Ostrom) refreshToken() (*oauth2.Token, error) {
-	uri := ostrom.URI_AUTH + "/oauth2/token"
+	uri := t.authUri("/oauth2/token")
 	data := url.Values{"grant_type": {"client_credentials"}}
 	req, _ := request.New(http.MethodPost, uri, strings.NewReader(data.Encode()), map[string]string{
 		"Authorization": t.basic,
@@ -225,7 +245,7 @@ func (t *Ostrom) run(done chan error) {
 			"zip":        {t.zip},
 		}
 
-		uri := fmt.Sprintf("%s/spot-prices?%s", ostrom.URI_API, params.Encode())
+		uri := t.apiUri(fmt.Sprintf("/spot-prices?%s", params.Encode()))
 		if err := backoff.Retry(func() error {
 			return backoffPermanentError(t.GetJSON(uri, &res))
 		}, bo()); err != nil {
diff --git a/tariff/ostrom/api.go b/tariff/ostrom/api.go
index 02dfa1813..e487f2279 100644
--- a/tariff/ostrom/api.go
+++ b/tariff/ostrom/api.go
@@ -14,8 +14,6 @@ const (
 	URI_API_SANDBOX      = "https://sandbox.ostrom-api.io"
 	URI_GET_CITYID       = "https://api.ostrom.de/v1/addresses/cities"
 	URI_GET_STATIC_PRICE = "https://api.ostrom.de/v1/tariffs/city-id"
-	URI_AUTH             = URI_AUTH_PRODUCTION
-	URI_API              = URI_API_PRODUCTION
 )
 
 const (