Trouble creating a record via API

Hey, I’m a non-programmer trying to wet my feet with a Landbot integration to Airbase. My webhook call from Landbot is working for every field except the “Contact” field which is linked to a field in a different table:

{"fields": 
    {
    "Status":"New",
    "Notes":"@notes",
    "Mortgage Type":"@mortgagetype",
    "New Purchase Price":"@purchaseprice",
    "Downpayment":"@purchasedownpayment",
    "Transfer Amount":"@propertyprincipal",
    "Equity Take Out Amount":"@equitytakeoutamount",
    "HELOC Amount":"@heloclimit",
    "Own Home":"@ownhome",
    "Current Home Value":"@propertyvalue",
    "Remaining Mortgage":"@propertyprincipal",
    "Monthly Mortgage Payments":"@propertymortgagepayments",
    "Monthly Property Taxes":"@propertytaxes",
    "Monthly Maintenance Fees":"@propertymaintenance",
    "Monthly Rent":"@monthlyrent",
    "Household Income":"@householdincome",
    "Household Debt":"@householddebt",
    "Household Debt Payments":"@householddebtpayments",
    "Contact":["@crm_id"]
    }
}

That’s the full JSON, but it’s failing for the last line (the other fields work create correctly)

I’m getting the following error message:

"No JSON response\nObject of type RelatedManager is not JSON serializable"

I’ve read a couple threads here that seemed to work for others, but didn’t work for me.

Any help would be greatly appreciated!

Thanks.