---
updatedAt: 2026-06-29T20:33:19.000Z
agentTools:
  projectIndex: https://developer.bill.com/llms.txt
---

# Upload customer attachment

Upload an attachment for an existing customer. The file size limit is 6 MB.

**Note**: When you upload an attachment, it takes a few minutes for BILL to complete the upload process.

See [Documents and attachments](https://developer.bill.com/docs/documents-attachments) in the Guides section for more information, sample requests, and responses.

# OpenAPI definition

```json
{
  "openapi": "3.0.1",
  "info": {
    "title": "BILL v3 API",
    "description": "BILL is a cloud-based financial operations platform for an organization's accounts payable (AP), accounts receivable (AR), and spend & expense (S&E) automation.\n\nThe BILL v3 API gives you access to the same infrastructure that powers the AP, AR, and S&E products. In addition, you can receive real-time event notifications with webhooks.\n\nThe BILL Developer Documentation is available at [developer.bill.com](https://developer.bill.com/docs/home).\n\n## Quickstart\nSign-up and generate a developer key for working with the BILL v3 API. With this key, you can build with the AP, AR, BILL network, and webhook workflows. See [Sandbox API sign up](https://developer.bill.com/docs/api-sandbox-sign-up) for more information.\n\n### Spend & Expense API\nAn API token is required for working with the Spend & Expense API. See [Authentication with Spend & Expense API token](https://developer.bill.com/docs/authentication-with-api-token) for more information.\n\n### BILL v3 API in Postman\nWith this collection, you have access to the BILL v3 API in Postman. When you save your sandbox API credentials as environment variables in Postman, you can simply refer to the variables when you are testing with the BILL v3 API. See [BILL v3 API in Postman](https://developer.bill.com/docs/bill-v3-api-in-postman) for more information.",
    "version": "1"
  },
  "servers": [
    {
      "url": "https://gateway.stage.bill.com/connect",
      "description": "sandbox"
    }
  ],
  "paths": {
    "/v3/attachments/customers/{customerId}": {
      "post": {
        "tags": [
          "attachments"
        ],
        "summary": "Upload customer attachment",
        "description": "Upload an attachment for an existing customer. The file size limit is 6 MB.\n\n**Note**: When you upload an attachment, it takes a few minutes for BILL to complete the upload process.\n\nSee [Documents and attachments](https://developer.bill.com/docs/documents-attachments) in the Guides section for more information, sample requests, and responses.",
        "operationId": "createCustomerAttachment",
        "parameters": [
          {
            "name": "sessionId",
            "in": "header",
            "schema": {
              "type": "string",
              "description": "API session ID generated with `/v3/login`",
              "nullable": true,
              "example": "{{session_id}}"
            }
          },
          {
            "name": "devKey",
            "in": "header",
            "schema": {
              "type": "string",
              "description": "Developer key generated with your BILL developer account",
              "nullable": true,
              "example": "{{developer_key}}"
            }
          },
          {
            "name": "customerId",
            "in": "path",
            "required": true,
            "schema": {
              "minLength": 1,
              "type": "string",
              "description": "BILL-generated ID of the customer. The value begins with `0cu`.",
              "example": "{{customer_id}}"
            }
          },
          {
            "name": "name",
            "in": "query",
            "required": true,
            "schema": {
              "minLength": 1,
              "type": "string",
              "description": "File name with extension. For example, to upload a PDF attachment titled `business_details`, set `name` as `business_details.pdf`.",
              "example": "business_details.pdf"
            }
          }
        ],
        "requestBody": {
          "content": {
            "application/octet-stream": {
              "schema": {
                "type": "string",
                "format": "binary"
              }
            },
            "*/*": {
              "schema": {
                "type": "array",
                "description": "Attachment file",
                "items": {
                  "type": "string",
                  "format": "byte"
                }
              }
            }
          },
          "required": true
        },
        "responses": {
          "200": {
            "description": "Upload customer attachment response",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/AttachmentResponseDto"
                }
              }
            }
          },
          "4XX": {
            "description": "List of errors.",
            "content": {
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/BdcError"
                  }
                }
              }
            }
          },
          "5XX": {
            "description": "List of errors.",
            "content": {
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/BdcError"
                  }
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "AttachmentResponseDto": {
        "type": "object",
        "properties": {
          "id": {
            "type": "string",
            "description": "BILL-generated ID of the attachment. The value begins with `att`."
          },
          "name": {
            "type": "string",
            "description": "Attachment name"
          },
          "createdTime": {
            "type": "string",
            "description": "Created date and time",
            "format": "date-time"
          },
          "downloadLink": {
            "type": "string",
            "description": "URL for downloading the attachment. Use the URL in a GET request to download the attachment."
          }
        },
        "description": "Attachments response."
      },
      "BdcError": {
        "required": [
          "category",
          "code",
          "severity",
          "timestamp"
        ],
        "type": "object",
        "properties": {
          "timestamp": {
            "type": "string",
            "format": "date-time"
          },
          "code": {
            "type": "string"
          },
          "severity": {
            "$ref": "#/components/schemas/Severity"
          },
          "category": {
            "$ref": "#/components/schemas/Category"
          },
          "message": {
            "type": "string"
          },
          "params": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/Param"
            }
          },
          "detail": {
            "type": "string"
          },
          "help": {
            "type": "string"
          }
        }
      },
      "Category": {
        "type": "string",
        "enum": [
          "REQUEST",
          "APPLICATION",
          "SERVER",
          "DOWNSTREAM"
        ]
      },
      "Param": {
        "required": [
          "name",
          "value"
        ],
        "type": "object",
        "properties": {
          "additional": {
            "type": "object",
            "additionalProperties": {
              "type": "string"
            }
          },
          "name": {
            "minLength": 1,
            "type": "string"
          },
          "value": {
            "minLength": 1,
            "type": "string"
          }
        }
      },
      "Severity": {
        "type": "string",
        "enum": [
          "ERROR",
          "WARNING",
          "INFORMATION"
        ]
      }
    }
  }
}
```