I don't think the meta version of Permissions-Policy ever got implemented. "http-equiv" isn't a magic "here's a HTTP header I forgot to mention" pixie dust.
Better stick to the actual recommendation of adding the header in the server configuration.
Whilst http-equiv is said to be an enumerated value, so far as I know in Chrome, it actually is "magic HTTP Header pixie dust": [0]
And whilst in Firefox parsing of the element is more spread out, they accept a very wide number of headers that aren't documented, and you'll find examples on MDN for any number of headers using http-equiv which aren't specified in the standard or on their docs for http-equiv itself [2] (For example, X-DNS-Prefetch-Control [1]).
This will generally be a HTTP Header. How you add that depends on your server/framework. (And will be well documented).
If you've only got a static site, then you can always fallback and use HTML to achieve the same thing with http-equiv, which gets added to the head element:
<meta http-equiv="Foo" content="things" />
For example to redirect to /foo after 3 seconds:
<meta http-equiv="Refresh" content="3; /foo" />
It's a little off the beaten track for most people, but the kind of knowledge a web developer can be expected to know, or know where to look in the documentation.
Hopefully that can help you in your future endeavours.
