If you want to add records to a linked record field, Airtable’s API requires you (by default) to add them by their record ID, not by their primary field name.

Airtable’s API also requires you (by default) to choose from an existing linked record that already exists.

If you want to add linked records by their primary field name or if you want to create new linked records, then you need to turn on Airtable’s “typecast” function when making your API call.

In Make’s Airtable automations, they refer to Airtable’s typecast function as “Smart Links”, so you need to turn on the “Smart Links” option at the bottom of the “Create A Record” module.

p.s. I am the top Airtable/Make expert in the community. If you have a budget for your project and you’d like to hire an expert Airtable/Make consultant to help you with any of this, please feel free to contact me through my website: Airtable consultant — ScottWorld 

@ScottWorld thanks for your reply.

I've added a search record module to get all the records ID available in the linked table (i.e. "Zone_Immobili"). 

here below table "Zone_Immobili"

The search records module has been set as shown below:

If I set the bundle limit to 40, the search module returns all the 39 records. 

Since I want to recall just one record, I've entered 1 in the limit field. 

Now I'm tring to set the filter with the aim to find the record ID associated to this condition:

CAP_ID = CAP (i.e. value returned by the Set Variable Tools)   

In other words, if the email body contains CAP: 20123, I expect that the returned CAP variable will be 20123. Then I want to filter the records to find the one associated to CAP_ID = 20123 

I cannot set the filter properly.

I would be grateful if you could help me.

Thank you 

You have to type a formula just like you would type it into Airtable.

Your formula CAP_ID = CAP would not work in Airtable, because it would need to look like this:

{CAP_ID} = "CAP"