I was refused a tourist German visa. Is it OK to apply for a business trip to the same place? [duplicate]

The first time, I was not entitled to disclose the purpose of the travel to anyone beyond the company, so I applied for a tourist visa.

It feels, er, not completely true, but I couldn't provide an invitation from the inviting company (we didn't even know if we will sign an agreement, and the deal was a top secret).

I was rejected with a reason like "not convincing".

Is it bad?

Now I'm applying for a business trip visa. update: for a different date, for 3 days. It is not the same trip, but happens within a month from 1st application.

Should I include an explanation letter to a visa officer? What should I write there to convince the officer?

Here's why I think I need to provide extra explanations (these are USA rules but still): "As per "The Homeland Security Act - 2002" [...] When the applicant applies again in the future, the consulate officer must review the prior notes for rejection reasons. If the officer decides to grant the visa this time, he/she needs to justify the reasons for overruling the previous decision and note the same in the system."