Synchronising Shopware customers with ERP using the API.. ID-issue

Hi there,

I’m trying to sync the customers in my ERP with customers in Shopware.
Obviously i’m using the examples like REST API - Examples using the customer resource

The problem is that i want to add a customer with a specific ID into Shopware like i’m able to with the articles.
This doesn’ seem to be possible as i’m also not able to use ?useNumberAsId=true.

My second idea was to add the ERP-ID to the comment field of the customer in Shopware.
But am I able to fetch the specific customer by it’s Comment-field value?
e.g. $client->get(‘customers/COMMENTFIELDVALUE=ERP_ID’);

I suppose i’d have to use the additional filters for the api but i’m having a hard time figuring out how it works.

Any help is much appreciated.