If you haven’t already, checkout the documentation at https://airtable.com/api . And if you’re able to post a screenshot or code snippet of what is actually making the call to the Airtable API that will help us provide more specific answers.
In order to update a linked field, you need to already know the record IDs of the records to which you want to create a relationship. So if you want to update a product record to be related to two Vendors, you would need to first fetch the two Vendor records and get their IDs. Then you can build your patch request payload so that it looks something like this:
{
"fields": {
"Name": "This is the new name",
"Other Field": "This is some other field",
"Vendor": [
"recrnsKSwhPp9WAao",
"recsSVeVF54yLRwC9"
]
}
}
This patch request would REPLACE whatever links the Vendor field had with links to the two specified vendors.