Site crashes after adding GSC code

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Hey

Let me start by saying that I am new here :)

I've been creating websites for a few years now, I do optimization and SEO but I haven't come across something like this.

A client asked me to optimize the site [DELETED]. I started by adding the Google Search Console tag to the header of the site and here was the problem. After saving, the page crashes. Both when I do it from within Wordpress and through the FileZilla client. What could be the cause? I should add that this is not the first time I am doing this.

What I have tried:

I've edited the header file through the wordpress theme editor, through hosting and through FileZilla.