There are several causes that can lead to errors with redirects to (some) iDEAL Issuers:

• iDEAL in mobile app: using in-app web browser for Issuer redirect
• Adjustments to the IssuerAuthenticationURL before redirect (e.g. trough encoding)
• Using POST in stead of GET for the redirect to the IssuerAuthenticationURL

In some cases you as a Merchant may experience customers that indicate they have made a succesful payment to you through iDEAL but in your systems no payment confirmation is visible. This might be a result of one of the following cuases: 

Relating to implementation of iDEAL in a mobile app, there are some specific issues that may occur:

In case of issues with certificates and signing, below explanation on certificate use may help