'The route template separator character '/' cannot appear consecutively. It must be separated by either a parameter or a literal value. Parameter name: routeTemplate' code example

Example: 'The route template separator character '/' cannot appear consecutively. It must be separated by either a parameter or a literal value. Parameter name: routeTemplate'

In my case, I had an extra '/' on my Route query string.

LIKE:

[Route("get/liked//{id}")]
[HttpGet("[action]")]
public async dynamic GetLikedPost(int id)

INSTEAD OF:

[Route("get/liked/{id}")]
[HttpGet("[action]")]
public async dynamic GetLikedPost(int id)