Invest Account Into Model

Submit invest or divest instructions for one or more accounts into a **single** destination model, with a **per-account** cash amount. Each entry in `accountList` pairs an account identifier with the individual `amtToInvest` value applied to that account (positive to invest, negative to divest). Constraints and comparison to `/fa/model/tws-invest-divest`: * Only a **single model** may be targeted per request (the top-level `model` field). To invest into multiple models in one call, use `/fa/model/tws-invest-divest` and its `modelList`. * The model must be denominated in a **single currency**; multi-currency models are not supported by this endpoint. Use `/fa/model/tws-invest-divest` for models holding instruments across multiple currencies. * FA pre-trade allocation **groups are not supported** here — each account and its individual investment amount must be listed explicitly in `accountList`. * Because each account is listed individually, this endpoint allows a **different investment amount per account**. `/fa/model/tws-invest-divest`, by contrast, splits a single `amtToInvest` equally across accounts when a `group` or `accountList` is used.