Details:
The following endpoint has a string length limitation when adding attachments to fields:
{baseURL}/api/rest/v1.0/materials/{eid}/properties?force=true
{status: '400', code: 'BadRequest', title: 'The request parameters are in bad format.', detail: '[ERROR - Unable to parse JSON - String length… exceeds the maximum length (20000000).: []]'}
The total size supported varies depending on the encoding used.
When adding large attachments, we recommend using:
/materials/{eid}/attachments/{fieldId}
This uses binary transfer, make sure you include a "filename" header which specifies how to you want to name the file.