post
https://your-protect-instance.example.com/api/rest/v1/tn/pledges//add_collateral
This endpoint adds collateral to an existing pledge. It will increase the amount of the pledge. The additional funds will also be reserved and can't be spent until they are unpledged or withdrawn by the target participant. Only the pledgor (owner of the pledge) can call this endpoint. The endpoint will create a pledge action that needs to be approved to finalize the addition of collateral.