Problem with URL rewriting and Error 404

Hi
I have the following problem, please need help.

URLs are defined in my default is "vBSEO"
Example: mysite.com/f2, mysite.com/f15, ....

What I want is to replace /f2 by the following /forum name:
Example: mysite.com/f2 = mysite.com/general

Then I set up URL rewriting in options "vBSEO" and then I added the following lines to the file ".htaccess":

# Forum
RewriteRule ^f([0-9]+)/$ vbseo.php?vbseourl=forumdisplay.php&f=$1 [L]
# Forum Pagination
RewriteRule ^f([0-9]+)/index([0-9]+)\.htm$ vbseo.php?vbseourl=forumdisplay.php&f=$1&page=$2 [L]
# Threads
RewriteRule ^f[0-9]+/.+-([0-9]+)\.htm$ vbseo.php?vbseourl=showthread.php&t=$1 [L]

Until then everything works without a glitch

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The problem I have after doing the above, is as follows:

1.- Before making changes, when the url was: misitio.com/f2
If a user enters a URL that did not exist, eg mysite.com/blablabla, my site returned the page "Error 404", just as I have it configured.


2.- After making changes, when the url is: misitio.com/forum name
If a user enters a URL that does not exist, eg mysite.com/blablabla, my site returns the following message:

"No Thread specified. If You Follow a valid link, please notify the administrator "

Why is this problem, I want to return the page "Error 404", as it was working before.

What do I have to do?
I have vBulletin 3.8.4

Hello,

you should remove all of that and just change your forum url formats within vbseoCP to use [forum_name] instead of f[forum_id]

That's what I did, but if I add those lines in ".htaccess"

When someone enters /f2, the website does not redirect to the forum /general