In LSP.expert, you don't convert a quote into an invoice. You create a job and then you create a quote and an invoice based on this job.
This is how it works:
You create a job
You create a quote based on this job (Actions > Create quote in the job) if your client asks for a quote
You define the quote as Accepted or Rejected
If the quote was accepted, you finish the job
Once the job is finished, you invoice it (to know how to create an invoice, see this article: https://help.lsp.expert/en/articles/742754-how-to-create-an-invoice.)
