Corrigindo o erro Attribute name “async” associated with an element type “script” must be followed by the ‘ = ‘ character no Blogger
Basta acrescentar =’async’ na primeira linha do Script.
Exemplo: Google Analytics
De:
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-SEUID"></script>
Para:
<script async='async' src="https://www.googletagmanager.com/gtag/js?id=UA-SEUID"></script>
Observação: Lembrando de alterar o UA-SEUID para seu ID no Google Analytics