With a Sandbox account restore purchases is not working.
It seems the sandbox tries to connect to "mzstorekit-sb.itunes.apple.com" but the server identifies itself with a wrong certificate. Normale purchases are working with the Sandbox-Account, but restore not.
It fails with the following message:
Restoring of transactions failed: Error Domain=NSURLErrorDomain Code=-1202 "The certificate for this server is invalid. You might be connecting to a server that is pretending to be “mzstorekit-sb.itunes.apple.com”, which could put your confidential information at risk." UserInfo={NSLocalizedDescription=The certificate for this server is invalid. You might be connecting to a server that is pretending to be “mzstorekit-sb.itunes.apple.com”, which could put your confidential information at risk., NSUnderlyingError=0x282aeaac0 {Error Domain=kCFErrorDomainCFNetwork Code=-1202 "(null)" UserInfo={_kCFStreamPropertySSLClientCertificateState=0, kCFStreamPropertySSLPeerTrust_desc=<SecTrustRef: 0xc7488fe60>, _kCFNetworkCFStreamSSLErrorOriginalValue=-9807, _kCFStreamErrorDomainKey=3, _kCFStreamErrorCodeKey=-9807, kCFStreamPropertySSLPeerCertificates=(
"<cert(0xc7404b200) s: mzstorekit.itunes.apple.com i: Apple Public EV Server RSA CA 2 - G1>",
"<cert(0xc7507c600) s: Apple Public EV Server RSA CA 2 - G1 i: DigiCert High Assurance EV Root CA>",
"<cert(0xc75055600) s: DigiCert High Assurance EV Root CA i: DigiCert High Assurance EV Root CA>"