composer.json invalid for Composer 2

The sgalinski/sg-cookie-optin package of which you are a maintainer has failed to update due to invalid data contained in your composer.json. Please address this as soon as possible since the package stopped updating.

It is recommended that you use composer validate to check for errors when you change your composer.json.

Below is the full update log which should highlight errors as "Skipped branch ...":

[Composer\Repository\InvalidRepositoryException]: Some branches contained invalid data and were discarded, it is advised to review the log and fix any issues present in branches

Reading composer.json of sgalinski/sg-cookie-optin (1.0.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.0.0) Reading composer.json of sgalinski/sg-cookie-optin (1.1.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.1.0) Reading composer.json of sgalinski/sg-cookie-optin (1.1.1) Found cached composer.json of sgalinski/sg-cookie-optin (1.1.1) Reading composer.json of sgalinski/sg-cookie-optin (1.2.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.2.0) Reading composer.json of sgalinski/sg-cookie-optin (1.3.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.3.0) Reading composer.json of sgalinski/sg-cookie-optin (1.4.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.4.0) Reading composer.json of sgalinski/sg-cookie-optin (1.5.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.5.0) Reading composer.json of sgalinski/sg-cookie-optin (1.6.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.6.0) Reading composer.json of sgalinski/sg-cookie-optin (1.6.1) Found cached composer.json of sgalinski/sg-cookie-optin (1.6.1) Reading composer.json of sgalinski/sg-cookie-optin (1.6.2) Found cached composer.json of sgalinski/sg-cookie-optin (1.6.2) Reading composer.json of sgalinski/sg-cookie-optin (1.6.3) Found cached composer.json of sgalinski/sg-cookie-optin (1.6.3) Reading composer.json of sgalinski/sg-cookie-optin (1.6.4) Found cached composer.json of sgalinski/sg-cookie-optin (1.6.4) Reading composer.json of sgalinski/sg-cookie-optin (1.7.0) Found cached composer.json of sgalinski/sg-cookie-optin (1.7.0) Reading composer.json of sgalinski/sg-cookie-optin (master) Importing branch master (dev-master) Skipped branch master, Invalid package information: Deprecation warning: replace.sg_cookie_optin is invalid, it should have a vendor name, a forward slash, and a package name. The vendor and package name can be words separated by -, . or _. The complete name should match "a-z0-9/a-z0-9". Make sure you fix this as Composer 2.0 will error.