Postal code requirement / validation

Good morning, 

We are integrating with Acumatica via its API, and have run into a situation w/regard to postal code. 

In the Acumatica UI, I can create a business account without entering a postal code. It doesn’t matter which country I specify in the address fields. 

Via the Acumatica API, I can create a business account without entering a postal code if I specify the country as France. But if I set the country to US and don’t enter a postal code, the response is a 422 error code specifying a problem with postal code. 

So it seems the postal code is required by Acumatica API if country = US, but there’s no similar requirement in Acumatica UI. Can any one please shed some light on this? I don’t know where requirements like this might be configured or if there’s a way we can work around this. 

Thank you, 

Dave