Make symbols work with otter.nvim

[RudolfVonKrugstein]

I am trying to make trouble work with otter.nvim, and as a first step I try to make the symbol/outline view work with a markdown file running marksman and otter-ls.

So, as said, marksman as well as otter-ls are running, and I type Trouble symbols. What I get is:

No results for **symbols**
Buffer: /home/me/test/test.md
Press ENTER or type command to continue

but when I do lua vim.lsp.buf.document.symbol() I get a quickfix window with the documents headlines (which is what I want)|

I wonder why this is and how I can fix this. Maybe `Trouble is asking otter-ls for symbols. which returns nothing and marksman is never asked?

If this is the case, can I somehow tell trouble that if marksman is present, that should be used for symbols?

Thanks!