I am using v.1.5.0 and testing EXPRESSCHECKOUT using sandbox env. I keep getting 10401 error when selecting express checkout icon. When looking at log file - AMT is 0 but total shopping cart is non-zero. I am only using GBP as my default cry and carry out transaction in GBP. My paypal is set to GBP too. Where did i go wrong....help! I bet it is some silly things i miss!!!!but don't know what that is.

Request Parameters: {SetExpressCheckout}
Array
(
[CURRENCYCODE] => GBP
[LOCALECODE] => US
[ALLOWEDPAYMENTMETHOD] => InstantPaymentOnly
[GIFTMESSAGEENABLE] => 0
[GIFTRECEIPTEENABLE] => 0
[GIFTWRAPENABLE] => 0
[GIFTWRAPNAME] =>
[GIFTWRAPAMOUNT] => 0
[BUYEREMAILOPTINENABLE] => 0
[CUSTOMERSERVICENUMBER] => 123456789
[BRANDNAME] => testbrand
[PAYMENTACTION] => Sale
[ALLOWNOTE] => 1
[LANDINGPAGE] => Billing
[NOSHIPPING] => 0
[REQCONFIRMSHIPPING] => 1
[AMT] => 0.00
[RETURNURL] => ************
[CANCELURL] => ************
[PAGESTYLE] => Primary
[METHOD] => SetExpressCheckout
[USER] => my sandbox
[PWD] => **********
[VERSION] => 61.0
[SIGNATURE] => ****************************************************BtmV
)

Response:
Array
(
[TIMESTAMP] => 2012-10-19T09:58:11Z
[CORRELATIONID] => 8dc8fc24434de
[ACK] => Failure
[VERSION] => 61.0
[BUILD] => 3926908
[L_ERRORCODE0] => 10401
[L_SHORTMESSAGE0] => Transaction refused because of an invalid argument. See additional error messages for details.
[L_LONGMESSAGE0] => Order total is invalid.
[L_SEVERITYCODE0] => Error
[CURL_ERRORS] =>
)

PAYPALWPP log:
Oct-19-2012 04:58:10 (1350640690)
getLineItemDetails 1
Not using default currency. Thus, no line-item details can be submitted.

Oct-19-2012 04:58:10 (1350640690)
ec_step1 - 1
Checking to see if we are in markflow
cart contents: physical

NOTE: $this->showPaymentPage = 0
Customer ID: 0
Session Data: Array
(
[securityToken] => a3edaa04d85ff7c90a74a35c9dbd88b6
[customers_host_address] => 46-64-73-246.zone15.bethere.co.uk
[cartID] =>
[cart] => shoppingCart Object
(
[contents] => Array
(
[31] => Array
(
[qty] => 1
)

            )

        [total] => 212.5
        [weight] => 25
        [cartID] => 69185
        [content_type] => physical
        [free_shipping_item] => 0
        [free_shipping_weight] => 0
        [free_shipping_price] => 0
    )

[check_valid] => true
[language] => english
[languages_id] => 1
[languages_code] => en
[currency] => GB
[today_is] => 2012-10-19
[updateExpirations] => 1
[session_counter] => 1
[customers_ip_address] => 46.64.73.246
[new_products_id_in_cart] => 31
[messageToStack] => 
[valid_to_checkout] => 1
[cart_errors] => 
[cart_country_id] => 209
[country_info] => Array
    (
        [countries_name] => Thailand
        [countries_iso_code_2] => TH
        [countries_iso_code_3] => THA
    )

[payment] => paypalwpp

)

Sathu:

[CURRENCYCODE] => GBP

PAYPALWPP log:
Oct-19-2012 04:58:10 (1350640690)
getLineItemDetails 1
Not using default currency. Thus, no line-item details can be submitted.

[currency] => GB

Looks like you've got your Zen Cart currency code for GBP defined as just "GB", and thus there's no correct match on currency codes, thus the price is getting translated to 0 (anything multiplied by 0 becomes 0).

Go to Admin->Localization->Currencies, and set your GBP currency code to GBP instead of GB

:jawdrop: how silly I am and I have been starring at it for 2 days pulling my hair out looking at various forums and still! :bangin:. Thank you DrByte, your prescribed med solve the problem.