Merchant Design Identification Error in PayPal Payflow Link
My Payflow Link integration has been giving some trouble recently. Whenever I attempt to start a transaction from my web shop, the following error occurs:

> Some required information is missing or incorrect. Please correct the fields below and try again.

  > - Error: Merchant Design Identification Error.

This happens immediately after being transfered to PayPal's hosted payment form. The account I am using is in test mode and the following values are posted to https://payflowlink.paypal.com/:

    LOGIN=[login]
    PARTNER=[partner]
    SHOWCONFIRM=true
    ECHODATA=true
    TYPE=S
    AMOUNT=99.99
    INVOICE=123456
    NAME=John Doe
    ADDRESS=Main Street 123
    CITY=Los Angeles
    ZIP=1234
    COUNTRY=US
    PHONE=
    NAMETOSHIP=John Doe
    ADDRESSTOSHIP=Main Street 123
    CITYTOSHIP=Los Angeles
    ZIPTOSHIP=1234
    COUNTRYTOSHIP=US
    PHONETOSHIP=

The [only result](http://www.magentocommerce.com/answers/discussion/471/Error-with-payflow-link/p1) Google has to offer for this error message suggests that the PayPal credentials aren't valid. This doesn't seem to be the case though, because when I send wrong credentials, I get a different error message, not this one. Also, I can log into PayPal Manager using these credentials and it doesn't report a 'deactivated account' status anywhere.

Has anyone else encountered this error message? And, more importantly, how do I fix it?
Merchant Design Identification Error in PayPal Payflow Link
===

My Payflow Link integration has been giving some trouble recently. Whenever I attempt to start a transaction from my web shop, the following error occurs:

> Some required information is missing or incorrect. Please correct the fields below and try again.

  > - Error: Merchant Design Identification Error.

This happens immediately after being transfered to PayPal's hosted payment form. The account I am using is in test mode and the following values are posted to https://payflowlink.paypal.com/:

    LOGIN=[login]
    PARTNER=[partner]
    SHOWCONFIRM=true
    ECHODATA=true
    TYPE=S
    AMOUNT=99.99
    INVOICE=123456
    NAME=John Doe
    ADDRESS=Main Street 123
    CITY=Los Angeles
    ZIP=1234
    COUNTRY=US
    PHONE=
    NAMETOSHIP=John Doe
    ADDRESSTOSHIP=Main Street 123
    CITYTOSHIP=Los Angeles
    ZIPTOSHIP=1234
    COUNTRYTOSHIP=US
    PHONETOSHIP=

The [only result](http://www.magentocommerce.com/answers/discussion/471/Error-with-payflow-link/p1) Google has to offer for this error message suggests that the PayPal credentials aren't valid. This doesn't seem to be the case though, because when I send wrong credentials, I get a different error message, not this one. Also, I can log into PayPal Manager using these credentials and it doesn't report a 'deactivated account' status anywhere.

Has anyone else encountered this error message? And, more importantly, how do I fix it?