The format used to search for a device by tag is shown below.

?tag=cof33cof3-coff-33co-ffee-123456789abc

Where cof33cof3-coff-33co-ffee-123456789abc is an illustrative example of a tag id.

http GET https://apps.dataplicity.com/devices/?tag=cof33cof3-coff-33co-ffee-123456789abc 'Authorization: Token 123456789abcdefghijklmnopqrstuvwxyzqwer'
curl --header "Content-Type: application/json" -H "Authorization: Token 123456789abcdefghijklmnopqrstuvwxyzqwer" --request GET https://apps.dataplicity.com/devices/?tag=cof33cof3-coff-33co-ffee-123456789abc

This will return devices that are assigned to this tag.