While being in test mode, I always get this fault message and no shipping rates are shown.

I checked my settings and keys and everything is filled in correctly.

I’ve put the plugin in debug mode and these are the debug messages:

FedEx REQUEST: Reveal

Array
(
    [WebAuthenticationDetail] => Array
        (
            [UserCredential] => Array
                (
                    [Key] => TvoAv4ULxiaIGGIa
                    [Password] => xMpsg1d8gWJyRPHfJanEF9zpj
                )

        )

    [ClientDetail] => Array
        (
            [AccountNumber] => 510087780
            [MeterNumber] => 118947744
        )

    [TransactionDetail] => Array
        (
            [CustomerTransactionId] =>  *** WooCommerce Rate Request ***
        )

    [Version] => Array
        (
            [ServiceId] => crs
            [Major] => 20
            [Intermediate] => 0
            [Minor] => 0
        )

    [ReturnTransitAndCommit] => 1
    [RequestedShipment] => Array
        (
            [EditRequestType] => 1
            [PreferredCurrency] => EUR
            [DropoffType] => REGULAR_PICKUP
            [ShipTimestamp] => 2017-10-24T00:00:00+00:00
            [PackagingType] => YOUR_PACKAGING
            [Shipper] => Array
                (
                    [Address] => Array
                        (
                            [PostalCode] => 10017
                            [CountryCode] => BE
                        )

                )

            [ShippingChargesPayment] => Array
                (
                    [PaymentType] => SENDER
                    [Payor] => Array
                        (
                            [ResponsibleParty] => Array
                                (
                                    [AccountNumber] => 510087780
                                    [CountryCode] => BE
                                )

                        )

                )

            [RateRequestTypes] => LIST
            [Recipient] => Array
                (
                    [Address] => Array
                        (
                            [Residential] => 
                            [PostalCode] => 8200
                            [City] => SINT-ANDRIES
                            [StateOrProvinceCode] => 
                            [CountryCode] => BE
                        )

                )

            [RequestedPackageLineItems] => Array
                (
                    [0] => Array
                        (
                            [SpecialServicesRequested] => Array
                                (
                                    [SpecialServiceTypes] => Array
                                        (
                                            [0] => SIGNATURE_OPTION
                                        )

                                    [SignatureOptionDetail] => Array
                                        (
                                            [OptionType] => NO_SIGNATURE_REQUIRED
                                        )

                                )

                            [SequenceNumber] => 1
                            [GroupNumber] => 1
                            [GroupPackageCount] => 1
                            [Weight] => Array
                                (
                                    [Value] => 0.5
                                    [Units] => KG
                                )

                        )

                )

            [PackageCount] => 1
            [CustomsClearanceDetail] => Array
                (
                    [DutiesPayment] => Array
                        (
                            [PaymentType] => SENDER
                            [Payor] => Array
                                (
                                    [ResponsibleParty] => Array
                                        (
                                            [AccountNumber] => 510087780
                                            [CountryCode] => BE
                                        )

                                )

                        )

                    [CommercialInvoice] => Array
                        (
                            [Purpose] => SOLD
                        )

                )

        )

)

FedEx RESPONSE: Reveal

stdClass Object
(
    [HighestSeverity] => WARNING
    [Notifications] => stdClass Object
        (
            [Severity] => WARNING
            [Source] => crs
            [Code] => 556
            [Message] => There are no valid services available. 
            [LocalizedMessage] => There are no valid services available. 
        )

    [TransactionDetail] => stdClass Object
        (
            [CustomerTransactionId] =>  *** WooCommerce Rate Request ***
        )

    [Version] => stdClass Object
        (
            [ServiceId] => crs
            [Major] => 20
            [Intermediate] => 0
            [Minor] => 0
        )

)