If your domain is registered with Squarespace, the steps are:
Click on Settings > Domains.
Under Squarespace Domains, click the domain name.
Click DNS Settings.
Scroll down to Custom Records.
In the Record field of a blank row, select TXT from the drop-down.
In the Host field, enter the host name they provided.
In the Data field, enter the TXT record value they provided.
Click Add to save the record to your settings.
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