Signing Session in iFrame Error

After creating a package, I get the session token for that package, and return the access signing URL which I pass to an iframe. The ceremony comes up but with this error at the top in a red box: “Unexpected error. We apologize for any inconvenience this may have caused you, please try again. If the problem persists, please contact our support team.” If I then click on the ACCEPT button at the bottom the following error pops up: “Unexpected token