Redirect htaccess rule giving 404 - .htaccess

Question

I have .htaccess file for seo friendly url. My standard url is;
index.php?p=user
And I can access this url by typing;
www.mydomain.com/user
Everything is fine until here. What I also want to do is to crate a seo url for the following url;
index.php?p=user&username=john
and the seo url should be as follows;
www.mydoamin.com/user/john
I have tried the following and it keeps throwing 404 error.
RewriteRule ^user/([^/]*)$ /index.php?p=user&username=$1 [L]
Can anybody tell me what is wrong here?
Here is the current .htaccess code
RewriteEngine On
RewriteRule ^(.+)$ index.php?p=$1 [L,QSA]
RewriteRule ^user/([^/]*)$ /index.php?p=user&username=$1 [L]

Answer 1

Considering the current configuration you added to the question the issue might be that you need to reverse the order of those directives:
RewriteEngine On
RewriteRule ^user/([^/]*)$ /index.php?p=user&username=$1 [L]
RewriteRule ^(.+)$ index.php?p=$1 [L,QSA]
The reason is that the directives get processed from top to bottom. That means that you need to implement more specific rules, so exceptions earlier, so further up in the file. Because the pattern ^(.+)$ will match all requests.
There are some additional modifications I would suggest. But you will have to test that, since I have only a very limited insight into your setup:
RewriteEngine On
RewriteRule ^/?user/([^/]+)/?$ /index.php?p=user&username=$1 [END]
RewriteRule ^/?([^/]+)/?$ /index.php?p=$1 [END,QSA]
In case you receive an internal server error (http status 500) using the rule above then chances are that you operate a very old version of the apache http server. You will see a definite hint to an unsupported [END] flag in your http servers error log file in that case. You can either try to upgrade or use the older [L] flag, it probably will work the same in this situation, though that depends a bit on your setup.
This implementation will work likewise in the http servers host configuration or inside a distributed configuration file (".htaccess" file). Obviously the rewriting module needs to be loaded inside the http server and enabled in the http host. In case you use a distributed configuration file you need to take care that it's interpretation is enabled at all in the host configuration and that it is located in the host's DOCUMENT_ROOT folder.
And a general remark: you should always prefer to place such rules in the http servers host configuration instead of using distributed configuration files (".htaccess"). Those distributed configuration files add complexity, are often a cause of unexpected behavior, hard to debug and they really slow down the http server. They are only provided as a last option for situations where you do not have access to the real http servers host configuration (read: really cheap service providers) or for applications insisting on writing their own rules (which is an obvious security nightmare).