When trying to transfer the call just drops

Could you please provide a call id?

6db05dae-3c89-4200-b30e-7cee84fe81ab

The call-ended-reason is that the assistant successfully forwarded the call from our side, but this could be an issue with the transfer sipVerb you are using in the transferPlan.

},
  "name": null,
  "destination": {
    "type": "number",
    "number": "+17254447868",
    "transferPlan": {"mode": "blind-transfer", "sipVerb": "refer"},
    "numberE164CheckEnabled": true
  },

You could try setting "sipVerb": "invite" or just removing "sipVerb" entirely.