Go mod replace dependency with private fork

I added the dependency to go.mod:

require (
	github.com/labstack/echo/v4 v4.3.1
)

replace (
	github.com/labstack/echo/v4 => example.com/echo/v4.git v4.3.1
)

And getting error like replace example.com/echo.git: version "v4.3.1" invalid: module contains a go.mod file, so major version must be compatible: should be v0 or v1, not v4. Tag with the required version exists in the repo.

While I'm tried to play with the version I got something like v1.2.1-0.20210520145606-2defe74d39f0, but when I set my replace section like:

replace (
	github.com/labstack/echo/v4 => example.com/echo/v4.git v1.2.1-0.20210520145606-2defe74d39f0
)

I'm getting the error errno=Connection refused related to the private git server.

Could you please advise what I'm doing wrong and how I can replace dependency with my private fork?

• Make sure your repo path is accurate. v4.git means the repo is called v4; if that’s true that’s ok, but if not replace it with the correct name of the repo and keep the v4.x.x tag after it.

• If the fork is private it’s probably not accessible by sum.golang.org. Make sure GOPRIVATE is set to your private fork so Go does not try to get the checksum.

  go env -w GOPRIVATE=example.com
  

If the replacement repo is hosted in a Git repository at example.com/echo, then the path to the replacement should probably be example.com/echo.git/v4:

replace (
    github.com/labstack/echo/v4 v4.3.1 => example.com/echo.git/v4 v4.3.1
)

If the example.com server serves go-import metadata, then you may be able to omit the .git suffix entirely:

replace (
    github.com/labstack/echo/v4 v4.3.1 => example.com/echo/v4 v4.3.1
)