是REST API端点和编码参数吗？

I'm still new to Go (and web programming in general) so apologies if I don't explain things properly.

I need my server to listen out for POST requests which will have four parameters. "Your REST API should expect the following parameters."

id int
con_id  string
key  string
fields  array

An example request would be:

uid=5&con_id=3456&key=6nD1a7EATbP7ewmZCpNkxzzyMvuIKqQQ&fields%5Bfield_ds_personal_details%5D%5B0%5D%5B%5D%5Baccess%5D%5Br%5D%5Ba%5D=1&fields%5Bfield_ds_personal_details%5D%5B0%5D%5B%5D%5Baccess%5D%5Br%5D%5Bs%5D=A

I'm unsure however how to properly do this in Go.

I've been using my endpoint as

api/user/{id}/{con_id}/{key}/{fields}

I can get it to work if I POST to

api/user/5/3456/hhjdd7887334jf but that's not how their API makes the request.

Using Postman and adding the parameters (so they're the same, encoded in the way the should be) I get a 404.

Any help would be very much appreciated! Even if it's just somewhere I can read more about how parameters in a request work.