This page covers how the Automaton should be used to renew domain names, it is an extract from the full documentation on Using the Automaton.

How do I renew a domain name through the Automaton?
A domain name is renewed by the RENEW operation.  This immediately triggers the processing of renewal for the specfied domain names.  Once submitted a renew operation cannot be cancelled, credit notes are not available if you renew in error.

How do I get a domain to renew automatically every two years?
This is accomplished through setting the 'auto-bill' field. The 'auto-bill' field can be set on a domain name with a value between 1 and 182, indicating how many days before expiry you wish to renew the domain name.  The field can be set for the life of a domain but will default to a null value and will be reset to a null value on tag change.  When the relevant point in time arrives, the domain will be positively renewed as if a positive renewal request has been received. 

The 'auto-bill' field can be changed or cancelled one clear day before the day indicated by the field value. Requests must be received by midnight.  Therefore if the 'auto-bill' field has been set to 10 for a domain name due to expire on the 20th of the month the 'auto-bill' field can be changed up until midnight on the 8th of the month.  To cancel an 'auto-bill' request set the field value to 0.

Note: The 'auto-bill' and 'next-bill' field cannot both be set.

How do I get a domain to renew automatically just the next time but not after that?
This is accomplished through setting the 'next-bill' field. The 'next-bill' field can be set on a domain name with a value between 1 and 182, indicating how many days before expiry you wish to renew the domain name.  The field is set for a single registration period only. When the relevant point in time arrives, the domain will be positively renewed as if a positive renewal request has been received and the field will be reset to a null value. 

The 'next-bill' field can be changed or cancelled one clear day before the day indicated by the field value. Requests must be received by midnight.  Therefore if the 'next-bill' field has been set to 10 for a domain name due to expire on the 20th of the month the 'next-bill' field can be changed up until midnight on the 8th of the month.  To cancel a 'next-bill' request set the field value to 0.

Note: The 'next-bill' and 'auto-bill' field cannot both be set.

How do I find out what domains on my tag need renewing?
The LIST operation has been enhanced in a number of ways to give you better information about when domains will expire.

What Automaton error message are specific to the renewal process?

V128 Domain name is not within its renewal period. 
A domain name can only be positively renewed 6 months in advance of the expiry date.  This message will be returned if you send a positive renewal request outside of this 6 month period. 

V129 Domain names may not be renewed when recur-bill is set to 'bc'.
When the recur-bill field is set to ‘bc’, it indicates that you wish Nominet to bill the registrant directly.  In order to positively renew a domain name, the recur-bill field needs to be set to ‘th’.  You can then submit a positive renewal request.

V134 Bad value for 'auto-bill' field (must be between 0 and 182).
The auto-bill field is used to indicate how many days before expiry you wish to renew a domain name.  You can set an auto-bill field on a domain name with a value between 1 and 182 where the value indicates the number of days before expiry that the domain name will be renewed. 

V135 Bad expiry '????????' specified for list action (must be of form CCYY-MM)
The date has not been entered in the correct format.

V136 Invalid expiry '????????' in list
The month specified is invalid.

V137 Both 'expiry' and 'month' provided for list action
This message is returned following a list request that includes both an expiry date and a month date. Only one should be provided.

V140 Auto-bill field may not currently be changed
It is not possible to change the auto-bill field if it is currently set to a value that would trigger positive renewal tomorrow, today or at some point in the past.   The auto-bill field value can only be amended before midnight, one clear day in advance of the day given as the field value.

V145 Auto-bill may not be set retrospectively
The auto-bill field cannot be set retrospectively so the value added to the field must be in the future.  If the expiry date has passed but you wish to renew the domain name, then you can simply submit a positive renewal request.

V151 Domain name has been paid for

V156 Domain name has been renewed

V157 Auto-bill and next-bill cannot both be set