Download Customer Id in invoice

Download Customer Id in invoice

Hi Zoho Books Representative, 

we have a problem with the platform and don't know how to solve it. 

>Our clients have a specific ID in our DSP and we would like to have it shown when we download all the invoices month to month. 

The problem is when we add this "Custom Field Value" it is not shown in the invoice. 

How can we solve it?

Thanks,