Disable domain checking during purchase

[NodoVIP]

Hello friends, this is my first post, I would like to ask you a question: 
I have a whmcs for a point project, we are going to manage this with only one "TLD", this "TLD" at the end is a short domain that I bought to configure it as tld in the system. What I need to do is to deactivate the availability check of the domain with "TLD" and continue with the next step, to choose the configured plan. 
I see that the system in the general settings has to validate if the domains that are already created so I would like to keep that, it may be useful. 
Thank you very much in advance. 
Regards