Paypal / Sandbox responses

I'm creating an online payment page to work with PayPal
Within the form, I have a return field specifying the return path.
This return field contains a dynamic variable.

When my page is sent to paypals Sandbox environment, paypal sends my page to the url specified in the 'return field'
However it doesn't contain any Paypal response codes.

When my page is sent to paypals live environment, the return url is augmented with the expected paypal return codes as expected.

What might be wrong with the SandBox environment that I need to know so I can test it properlly
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joomlaAuthor Commented:
Suspect it's because I have an incorrect 'auth_token'
But I don't know how to set an auth_token in Sandbox

Can anyone help
joomlaAuthor Commented:
No, its not the auth_token
I realised how to do that and it didn't address the issue.

I removed the dynamic return field and added a hidden static return field
Still, Sandbox failed to return the variables needed to process the data at our end.

Any help appreciated
sorry if this is a wasteful post, but trying to better understand it here:

so you send the payment details to the sandbox of paypal,
it then redirects you to a page on YOUR site then displays the infomation from the paypal payment?
joomlaAuthor Commented:
after payment appears to be accepted, the client is sent back to the calling site where it presumably checks the auth_token to be cerain that it should continuel

but it doesn't appear to be working.
in production, it sends back a url with codes and responses
in development it doesnt'

and when I test the status it says 'fail' even though paypay accepted the payment
joomlaAuthor Commented:
I'm going to close this.
I've been shown how to enable autoreply and set the auth_token for each individual buyer in sandbox.
This addressed my issue

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