It is not necessary to have a rating code to play rated chess. If you explain to the organisers, there should be no problem. Indeed, one way to get a rating code is to play in an event. A code will be created when the results are submitted. However there is another route as set out below.
The rating system receives an automatic update from the membership system every night. This will immediately update the displayed membership status of every member for whom the cross-reference from membership number (e.g. ME123456) to rating code (e.g. 987654A) is in place. If the rating system is not aware of which rating code the membership number applies to, either because it is a newly-issued membership number or because the reference has been mislaid, then the update takes longer.
There is a manual process to extract the data from the membership system and run it through the rating system to either assign a new rating code or match the membership to an existing one. This is done at an absolute minimum of once a month, immediately before the month-end rating calculation, usually at least once more in the middle of the month, and even more often if the number of new members warrants it. The best way for those who have previously been members to get their status updated promptly is to renew with their existing membership number.
Following a recent update this is now displayed in the rating system profile. Please note – during the process of assigning rating codes, if a member has not selected a club then the process will assign a geographic club code based on their postcode.