# Third Party Support

Gemini allows OMS/OEMS firms to send orders on behalf of existing Gemini accounts after signing a **service bureau agreement**.

Once the agreement is signed, **Gemini provides a unique CompID** for the account. The OMS/OEMS should use this CompID in the [OnBehalfOfCompID `<115>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_115.html) field of the [header](/trading/fix/overview/standard-header):

- The customer's Gemini account identifier is used in [OnBehalfOfCompID `<115>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_115.html)
- The third-party firm identifier is used in [SenderCompID `<49>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_49.html)

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### Required Fields for Third-Party Messages

The following messages require **both** [OnBehalfOfCompID `<115>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_115.html) **and** [SenderCompID `<49>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_49.html):

- [New Order Single `<D>`](/trading/fix/order-entry/exchange-bound-messages/new-order-single-limit) for submitting orders on behalf of that account
- [Order Cancel Request `<F>`](/trading/fix/order-entry/exchange-bound-messages/order-cancel-request) for canceling orders on behalf of that account

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### Execution Report Echo Fields

When Gemini sends an [Execution Report `<8>`](/trading/fix/order-entry/client-bound-messages/execution-report) in response to one of these messages:

- It echoes back the [SenderCompID `<49>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_49.html) value in the header
- The value originally in [OnBehalfOfCompID `<115>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_115.html) is placed into [DeliverToCompID `<128>`](https://www.onixs.biz/fix-dictionary/4.4/tagNum_128.html)

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See [Drop Copy: Third Party Support](/trading/fix/drop-copy/party-ids-&-roles/third-party-support) for details on Drop Copy third party support.