I\'ve created a test template within the DocuSign sandbox in preparation for some automation with another system. I\'m trying to populate these custom fields as there will be dy
DocuSign uses the term "custom fields" in (at least) 3 different ways:
Envelope Custom Fields let you specify metadata that gets associated at the Envelope level. This data isn't visible to recipients; it's just extra metadata that you can associate with an Envelope and query later (via API). See here for more info.
Document Custom Fields let you specify metadata that gets associated at the Document level. This data isn't visible to recipients in any way; it's just extra metadata that you can associate with a specific Document and query later (via API). See here for more info.
Custom Fields (aka "custom tabs") let you create (and save) your own customized tabs for use in your documents -- see here and here for more info.
Based on the information you've provided in you're question, I'd guess that you're using the term "custom fields" to refer to the tabs you placed throughout the document(s) in the template, some of which you want to dynamically populate with data via API when the envelope gets created, and others that recipients will populate with data during signing. Is that correct?
If this is what you mean, you can get a list of tabs (fields) that a specific recipient owns by executing a List Envelope Tabs request, as described here.
GET /v2/accounts/{accountId}/envelopes/{envelopeId}/recipients/{recipientId}/tabs
To retrieve tabs for a template (rather than an envelope), use this same URI, but specify the Template ID value in place of {envelopeId}. Also, note that the value that you specify for {recipientId} should identify the recipient who "owns" the tabs in the template/envelope. (Each tab in a template/envelope is "owned" by a specific recipient.)
If I've misunderstood your issue (or what you mean by "custom fields"), please comment on this answer and I'll attempt to clarify further.