Connecting Infusionsoft with X-Cart


We’re having difficulty connecting Infusionsoft with an X-Cart site (to link the newsletter sign-up box with Infusionsoft). We sent the code generated by Infusionsoft to the X-Cart support who replied:

"I have implemented the changes.
However, I faced the following error:

Failed to load No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘’ is therefore not allowed access.

That means that your store at msmshop is not allowed to perform requests to
If possible, could you please check the settings in your account at Infiusionsoft? Probably, msmshop should be added there as an allowed origin.
Please let me know the results."

We changed a setting in the Infusionsoft admin (published the Newsletter Signup form) and asked them to try again. They did and replied:

"Unfortunately, the same error still occurs:

However, I also received the subscription email from “The MSM Shop”:

subject: Welcome, Friend

So, it seems that the form is working fine, but that error is produced by Infusionsoft for some reason. It seems that they should send the ‘Access-Control-Allow-Origin’ header in responses.
If possible, could you please check the settings there (or, probably, contact their support and ask them to look into the issue)?"

Can someone help with this? Infusionsoft chat support referred me here.