First client: they don't want to spend in new content nor backlinks but still want a ranking plan soon

Hi,

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I've recently landed my first client through an old friend that has a small agency. So far I've given only short consults and SEO audits to small businesses. This client is a bigger one and wanted a complete package to increase their traffic within 3 months. I fixed some of their technical SEO issues in the first week but for some that the developers deemed "impossible".

They have no immediate plans to write more content for the site. Nor any to make some outreaching campaign for getting new backlinks (they have really a dire situation here). No activity on social media is planned either. They want a plan on how to rank in 3 months without new content and backlinks and I don't know how to put it for them that the traffic gains will be negligible without a serious investment in SEO.

How would you play this?

Thanks a lot and sorry for the newbie question :)