Symptoms
Unable to add keywords at SEO Toolkit > example.com > Add Keywords with the following error:
Keyword limit reached. Upgrade your license to increase the limit.
Keyword limit is reached. Please contact your administrator.
Cause
Free SEO Toolkit version contains only 5 keywords.
If one/several customers already used all the keywords, other customers won't be able to add it.
Resolution
Buy a paid SEO Toolkit license to switch to a plan with more keywords available. For example, Personal with 35 keywords.