Hi
I send you by mail the info for the backend
Here is the mail from return of the Crédit mutuel
"We confirm that there is an error when we call your interface return URL. We have a "Curl 51" message (error checking of the certificate).
Your key is the SHA-1 format. Anyway the data you use is fair (No. TPE, company code, key), otherwise you would already have an error message upon arriving at the payment page.
By testing the interface return you URL we had provided, we also get an error message related to the certificate. This is by doing a test on Internet Explorer and Firefox.
The concern lies at the level of the certificate that you use for your interface return URL.
We invite you to copy your URL in a browser to view this message.
Please check this page for example, certificate see pass the page to ask us to change the format of the URL and HTTP."
Thank you
Manuel