As most users know, and most definitely users who register .NL & .DE domains through WHMCS, WHMCS only knows annual periods for invoicing domains.
.NL & .DE domains have the possibility to be either registered/renewed for 1, 3 or 12 months. On the images below is specified what the exact numbers per TLD are.
Both the TLDs above are the only TLDs who offer these periods for registrations/renewals. Since WHMCS only knows annual invoicing periods, this can cause inconsistencies between the expiry date in WHMCS and the actual expiry date at the registry, and it will cause domains with a smaller period than annual to be excluded from the domain sync in WHMCS.
Currently we're investigating the possibility's to automatically change the registration period for .NL & .DE domains to an annual period. In version 1.1.1 of our module, we've already ensured that all transfers and creates through WHMCS are forced to an annual period and auto_renew is set to false for the domain as soon as it enters your Realtime Register account.
Further development to offer an option to change periods for domains which entered your WHMCS environment and Realtime Register account before the 1.1.1 module release are currently being investigated. If you feel the need to start changing the periods in Realtime Register before we finish research and development to build the functionality in our module, check out the knowledge base article with an instruction for this.