Why do I get the error "CNAME and other data" when trying to add a CNAME record?

Question

Why do I get the following "CNAME and other data" error when trying to add a CNAME record?

CONFIG_TEXT: Error: The DNS zone file is invalid. (Line #: domain.tld: CNAME and other data)

Answer

This error occurs when you are attempting to create a DNS record that is already defined by a CNAME record, or that a CNAME you are attempting to add conflicts with another record. This means that unlike other DNS record types, a CNAME record's name must be unique as this ensure that the data for the canonical name and its aliases are not different.

To resolve this issue, either remove the conflicting record, or if possible, change the name of the record you are attempting to create.

Note: The zone apex (records that share the same name as the zone itself, "domain.com" for example) cannot be set as a CNAME record. For more information please visit the following:
CNAME at the apex of a zone