Hi Peter
To resolve your SSL certificate issue please reinstall your signed certificate and private key but also include the 'bundle' certificate. When you download your signed certificate from GoDaddy’s customer portal there is a second file included in the zip called ca-bundle.crt. Many other providers require you to download their root and chain certificates individually, but GoDaddy make things a little easier.
When reinstalling your certificate, please ensure the content of the bundle file is dropped into the CA Root box within the Foldr Settings > Certificates installation screen. As mentioned in rpettit's message you can leave the 'Intermediate Certificate Chain' box blank as the bundle contains both the root and intermediate chain in one.
Hit 'Save' and after 60 seconds your certificate should now validate successfully on all devices, including iOS when using the app.
You can verify your certificate installation by using an online SSL checking tool such as this https://www.sslshopper.com/ssl-checker.html
If anyone needs help with this (or anything else Foldr related!) please drop me a PM or an email.
Cheers
Mike