This has been resolved with the Airtable support staff. I thought it would be good to post the resolution here for anyone else that might run into this.
What I found out was…
I ran a few more experiments and I found something interesting. If the field used in the filterByFormula command is a Link to Another Record field. It fails when a comma is used. My “Customer” field in the Websites table is a Link field. Every search for a string with a comma fails. This isn’t a matter of properly encoding the URL. It just doesn’t work. I think this is a bug. If I remove the comma from the field in the database and then remove the “,” or “%2C” from the URL string, the correct record is returned. By adding the comma back in both places, it returns an empty record set, {“records”: }.
To further troubleshoot this issue, I modified the URL to query the Customers table and directly search the “Company Name” field, which is a Single Line Text field. The query works with a comma in it.
Resolution from Airtable Support:
In order to escape the internal commas, I wrapped the search term for each individual record in double quotes, and wrapped the entire search string in single quotes:
{Field 20}='"Success Team, Weekly"'
Where {Field 20} is a linked record field, with linkages to a record named Success Team, Weekly
You could extend this, since it’s possible to search for a single record linked to multiple, e.g.,
{Field 20}='"Success Team, Weekly","Success Team, Monthly"'
And so we need to wrap each individual record in double quotes while wrapping the entire search string in single quotes.
