File Extensions for SS3.6

Questions
1

SS3.6

Multiple File Extensions

I want to add multiple file extensions to my website so these can be uploaded. When I put the code (example 1) in the yml file (this stuff is new to me) it works perfectly but I need to add more than one extension. When I add more than one as in example 2, it breaks. What am I doing wrong?

example 1:

File:
  allowed_extensions:
    - pes

example 2:

File:
  allowed_extensions:
    - pes
    - dst

To be exact, I need 13 different extensions. These are embroidery files if you need to know.
Any help is greatly appreciated.