Is your domain relatively new? It might be that Google's automated systems don't yet "trust" it due to a lack of history/backlinks, or it could be similar to a flagged domain from the past. This might be why they're suggesting you switch to a different domain.
To improve this, you could work on building more "authority" for your domain by gaining backlinks, which could help increase its trustworthiness. If time is an issue, you might consider purchasing an existing domain with a solid reputation. There are also some SEO tools which can give you insights into a domain.
To improve this, you could work on building more "authority" for your domain by gaining backlinks, which could help increase its trustworthiness. If time is an issue, you might consider purchasing an existing domain with a solid reputation. There are also some SEO tools which can give you insights into a domain.